Created by Matt Garvey
Original version 2009, revised and expanded 2024–2025

Introduction

How does one identify an episode of television? There are usually several options, and the answer depends on who is identifying it, for whom, and in what context. For example, is it a viewer, creator, broadcaster? Is it to create a schedule, discuss a plot, etc.?

Most episodes of scripted TV have official titles. Those titles often appeared at episodes' beginnings, far more commonly in the early days of TV, and they began falling out of use long before online listings and other electronic resources made it easy to find a given one. Some printed guides had them, but for decades many viewers would never know episode titles of their favorite shows, let alone that titles existed. (Look at a list of Friends episodes to see one play on this uncertainty.) Titles may vary (and lose puns!) in translation, making them hard to rely on or understand. They can change during production and even after release (or have dual either/or, AKA titles). And they're often cumbersome for brevity and official use among broadcasters.

Season-episode numbers are short and sweet, but they can be ambiguous for a variety of reasons. Are these in production or air order, or maybe a special DVD order? Does a double-length two-part episode count as one or two? Did the episodes air in a different order in another country, or were some skipped entirely? Are the season boundaries defined the same way by everyone? Sometimes the first episode broadcast is advertised as a special or preview, with the second episode being the "series premiere", so which is the "first episode"? And for a series in progress, particularly among the production staff making the darn thing, how can air order be known for certain? (Also, is episode "one-oh-two", for example, the second episode of season 1, or the 102nd episode?)

Production codes lend both certainty and brevity to episode identification. Most if not all scripted TV shows have some code system to keep things straight, from script writing through production and broadcast. The system may just be the series name and season-episode number, run together like a hotel room number (101, 203, 522). Or it may be a more elaborate system shared by many shows at a single production company, with no shows' episode codes overlapping, at least within a reasonable time frame, say a decade or so. These are primarily useful for the production and broadcast side, but if the codes are made available, say by putting them onscreen for viewers, they can be useful to everyone. Official but offscreen codes offer little advantage and can still lead to ambiguity. (I also admit that onscreen codes aren't always perfect; on occasion they are incorrect, or the wrong set of credits is played, and sometimes they're just illegible!)

The Simpsons is one of the shows that use distinctive production codes (unique-ish within 20th Century Fox Television/20th Television) and include the codes in the credits for all to see. The mass appeal and longevity of the show combined with the vocal group of nerds among its fans have made the use of production codes as a primary identifier (or shorthand, especially to those with good memory) a stamp of Simpsons nerddom; few series seem to inspire the rabid latching-on to codes by fans for quick episode reference, The Simpsons and Star Trek (whose numbers aren't even shown) being primary in my mind. The show itself has recognized this quirk and had fun with it, often including production codes in DVD commentaries (and all DVD booklets since season 2), on occasional merchandise, and in jokes in episodes.

Additional advantages to fan use of these codes include incredible brevity in lists and grids, and the ability to view Simpsons trends, evolution, and oddities by production order rather than air order. (For example, observing from 2F16 and 2F20 that "Who Shot Mr. Burns?" was not originally planned as two parts.) Episodes on undated recordings can be identified easily. Greater familiarity gives codes some meaning at just a glance. But they're not very self-explanatory, and can be very confusing or daunting to the uninitiated; any single episode's code can be found and used, but why does 4F02 come from season 8, while 7F08 is from season 2, and where did CABF14 get so many letters? When a similar set of letters and numbers shows up in another 20th Century Fox show, how is it related?

Fortunately, it's not hard; it's fun! This document aims to demystify it all for you, with Simpsons-specific information at the top and then the broader system(s) it fits into. So join me, won't you?

Table of contents

The Simpsons production codes

• Quick reference
• Appearance
• What the codes mean
• Oddities and special numbers
• References in the show

The Simpsons production codes

Quick reference: codes by production season

If you just want to see what a code means, or refresh your memory, or look for a trend all on your own, start here. These are production seasons; not only are episodes often broadcast slightly out of order, most seasons leave a few episodes for the next air season (or two!). A full list of episodes in air order is here, but in short:

Season 1:    7G01-13
Season 2:    7F01-24
Season 3:    8F01-24
Season 4:    9F01-22
Season 5:    1F01-22
Season 6:    2F01-22, 2F31-33
Season 7:    3F01-24, 3F31, 3G01-04
Season 8:    4F01-24
Season 9:    5F01-24
Season 10: AABF01-23
Season 11: BABF01-22
Season 12: CABF01-22
Season 13: DABF01-22
Season 14: EABF01-22
Season 15: FABF01-23
Season 16: GABF01-22
Season 17: HABF01-22
Season 18: JABF01-22
Season 19: KABF01-22
Season 20: LABF01-20
Season 21: MABF01-22
Season 22: NABF01-22
Season 23: PABF01-22
Season 24: RABF01-22
Season 25: SABF01-22
Season 26: TABF01-22
Season 27: VABF01-22
Season 28: WABF01-22
Season 29: XABF01-22
Season 30: YABF01-22
Season 31: ZABF01-22
Season 32: QABF01-22
Season 33: UABF01-22
Season 34: OABF01-22
Season 35 and beyond: 35ABF01-22, etc.

The Simpsons Movie, of course, has no television production code. It's just "the movie". (Its serial MPAA certificate number is 43622, for what it's worth.)

Some oddities are already evident, but they will be explained.

Appearance

These codes always appear on the copyright page in the credits. Format and placement (quotes mine):

• 7G08 (1st episode broadcast) as a simple "7G08" in the last line of some midscreen legalese, after the period, a fittingly 80s style for the only episode broadcast in the 80s.
• 7G02, 7G03, 7G04 as "THE SIMPSONS EPISODE NO. 7G02" etc. on a line of its own above the copyright notice.
• From 7G05 (5th aired) to OABF13 (air season 34 finale), "THE SIMPSONS EPISODE #7G05" (same place above copyright) and so on. (The lone double-length episode in season 28 uses "THE SIMPSONS EPISODE #WABF04 & #WABF05" when not split into halves.) This style helps make the existence of the code less cryptic, and it was used by a handful of other shows (most others being animated series?). It predominated for over 700 episodes with premiere dates ranging from 2/4/90 to 5/21/23, including the late-premiering 7G01.
• Since the beginning of air season 35 (10/1/23), with some company-wide rearrangement of the copyright screen, it's now simply "Production #OABF18" and so on, around the same place on the screen, under copyright and all-rights-reserved. (The next double-length episode updates the format: "Production #35ABF21 & #35ABF22". Technically this appears in all caps, but that's how that one formats the credits overall.) This is a more common style in the 21st century, and other shows transitioned around the same time too. But it's a little more boring and less customized.

What the codes mean

Simpsons production codes can be difficult to follow in part because they span three code traditions from 20th Century Fox Television. Further complications arise from extra twists (numerical discontinuity, the 3Gs, etc.). In short, all Simpsons episode codes consist of a prefix designating the production season and two digits indicating the episode number within that season. All prefixes except 7G and 3G can be further broken down into a year/season signifier and a characteristic letter or group of letters marking it as The Simpsons (F or ABF).

Season 1 (7G): tail end of the 80s. As illustrated below, the 20thCFT system of code prefixes at this time, while more orderly than its predecessors, was still mostly a random collection of digit-letter combinations. For example, The Tracey Ullman Show used 4W and 5W for the episodes that spawned our favorite family. Its next season was 7W, possibly because there was a gap in time, but the show had no claim to the letter W, or to a number near 4 or 5, even if renewed shows tended to get similar codes for new seasons and a lot of 5s-7s were in use at the time. The point is that "7G" cannot be broken down further. It simply means "season 1 of The Simpsons", which was 1989-90. Had this system continued, season 2 might have been 8G, or 8F, or 7L.
Looking at episode production codes in season 1 also clears up some confusion about what the "first" episode is, or at least eliminates one common nominee. 7G01 is the first episode in production order; originally the show was meant for a fall 89 debut but the animation coming back (mostly for the first episode) was not good, and a lot had to be redone. The whole season slipped, and 7G08, suitably numbered to land at about Christmas, and ready in time, was the first episode to air, followed by 7G02 four weeks later and so on, now with fixed animation. 7G01 wound up airing last of the 13 7Gs. But 7G08 was branded as "The Simpsons Christmas Special" onscreen, and the series was advertised as beginning in January 1990, creating the impression that a one-off special led to the creation of a whole series and 7G02 was the first real episode, with 7G08 just grandfathered in. This is obviously untrue. (It's also incorrect to call any of these episodes a pilot. This is discussed below.)

Season 2-9 (7F-9F, 1F-5F): the more orderly 90s. Before the season 2 codes were assigned, 20thCFT instituted a more rigorous system. Prefixes were still digit-letter combinations, but now each digit would refer to the calendar season (starting with 7 for 90-91, wrapping from 9 to 1, etc., ending with 5 for 97-98), and each letter would consistently represent one show (F = Simpsons). As shows were cancelled, their letters could be recycled, but within a show's lifetime the letter would be its own, and the digits applied to all series. It's a little confusing to go from 7G to 7F, but 7G couldn't be reused, and at least two other shows had similar 7-7 transitions; had this system begun a year earlier, perhaps season 1 would be 6F (or 6G, then 7G for season 2, etc.), and had it continued for one more year instead, season 10 would almost certainly be 6F. As it is, there are no 6F episodes, and of course no 0F either.

Season 7 special episodes (3G). Four extra episodes were produced by earlier showrunners Al Jean and Mike Reiss, bearing season 7-style codes, though they did not air until season 8 and 9. In this case, 3 means the calendar year matching season 7, and G seems to be used for its proximity to F and/or precedent of 7G. More on these in numbering oddities below.

Season 10-31 (AABF-ZABF): 21st Century Fox. Around early 1998, 20thCFT switched to yet another system, and I like to think the longevity of The Simpsons played some part in that. (After all, it could recycle characteristic letters for a while, trying to avoid duplicates, but if Simpsons season 10 were 6F, season 11 couldn't be 7F again!) Now, prefixes would be 4 characters instead of 2: the first to refer to the season number of the series (not the absolute calendar year), then three letters to identify the series, drawn on a sequence like license plates. The Simpsons is "ABF", and that means what "F" used to before. It even kept the "F" (and not all series got that courtesy!).
However, since the switch was made for season 10 (for some official season 9 stuff, see oddities below), letters continued the numerical sequence, thus season 10 is A+ABF+01=AABF01 and so on. 10 is A, 11 is B, etc. In isolation, it appeared that things had gone 4, 5, AAB, BAB..., and it was a little confusing at first. Since ABF is its own atomic unit and does not change, reading these codes aloud is best done with emphasis on the first letter, a quick ABF without stress, and then the episode number itself with some emphasis; pronunciations like "DAB-F06" (as heard in episode DABF15) aren't really right.
The letters I, O, Q, and U are skipped in the season-number lettering to avoid confusion, or they were at first. The alphabet is already a bit of a stopgap, but who could use it all up by getting past 31 seasons?

Season 32-34 (QABF, UABF, OABF): exhausting the alphabet (almost). What comes after the letter Z? I pondered many options, but either the producers or someone at 20th Television (not 20thCFT for long: coincidentally, the Disney/Fox deal happened around this time!) settled on returning to the forbidden letters. This already makes things confusing for sorting, but even these letters are used out of order: QUO. And the letter I remained unused. (At least either way there's a handy mnemonic device.) The reason for all of this is unclear, but my guess is that the show was not expected to continue long enough to break this patch too; renewals occurred for pairs of seasons and codes seem to have been allocated at that time, a theory that does more to explain the abandonment of I than the order used here, since it would result in Z and Q for one renewal, then U and O for the next. O and I were the least desirable letters for their obvious resemblance to 0 and 1; perhaps U was still promoted just in case a sudden end spared O. On the plus side, with high definition, better credits presentation (for The Simpsons anyway) on Fox and in syndication in recent years, etc., these tricky letters are easier to make out than they used to be.

Season 35 and up (35ABF, etc.): back to numbers. After all that messing about with leftover letters, and in fact using the alphabet in the first place, it just went to a 2-digit year, and here it seems destined to stay. (Was I skipped because it was completely off limits, or because the February 2023 renewal for seasons 35 and 36 would otherwise have created I and 36?) At least this, for the first time in Simpsons history, creates a pretty obvious code.
In retrospect, though, it probably would have been wiser to go from ZABF to 32ABF. But we're stuck with these unsortable codes now (eat your heart out, 9F-1F!). Some might say even 10ABF to 31ABF would have been better! (Having often dropped the ABF in shorthand notes, for episode designations like P07, and now being faced with the production/air order ambiguity of, e.g., 3501, I do think the core letter system has a certain advantage. Wherever letters are used, purely numeric interpretation is impossible.)

Now that The Simpsons has blazed the trail for other long-running shows (which transitioned uniformly from 9 to A), it will be interesting to see whether they match the new wrinkles. As I write this update in summer 2025, Family Guy has jumped from its NACX production season to PACX. Will it use any of the other QUO letters in its alphabetical sequence or after Z? Will ZACX lead to, say, 31ACX (as discussed below, it skipped G!), or will it also grasp at straws for a few more years with unused letters? Time will tell. My hunch is Q and U may get used in order but probably won't, and ZACX will go to a 2-digit number + ACX.

It's funny to see how the show has not only spanned 3 code styles, but stretched two of them to their limits, arguably breaking the last one, or at least the season character of it. Still, that system held strong for over 20 years (and still manages pretty well with modifications), a feat that shames the older ones, which will be explored below.

Oddities and special numbers

Seasons six through nine of The Simpsons had a number of numbering quirks with hidden logic. It may be especially helpful to refer to air order to see how these episodes fit in.

• Clip shows (specifically, the 2nd through 4th of a total of 5), although considered real episodes, tend to have higher episode numbers. 2F33 and 3F31 leave sequence gaps and aired near the beginning of their production seasons (2F33 in particular may have been produced on extremely short notice, with episode numbers 31 and 32 already in use, see below, yet was also the first 2F episode to air), but share producers with the normal 2F and 3F episodes. 5F24, described in a later note, has some resemblance to this pattern. (9F17 and DABF12, the first and last clip shows, have nothing special about their numbering, air order, etc.)
• Several other episodes use high numbers to set themselves apart. In production season 6, which was executive produced by David Mirkin (2F01-22, 33), 2F31 (the crossover episode with Al and Mike's The Critic) and 2F32 were co-executive produced by former showrunners Al Jean and Mike Reiss (with Mirkin), and they aired in the middle of the season.
• Special episodes produced alongside season 7 (3F01-24, 31) did not get extra high numbers, but just a whole separate code prefix: 3G01-04. While the 3Fs were executive produced by Bill Oakley and Josh Weinstein, these were done by Jean and Reiss instead. These extra episodes ran during air seasons 8 and 9, beginning just after the 3Fs had finished. Why they weren't 3F25-28, or 3F32-25, I could not say. In some sense, the "G" marks them as almost a separate show, but perhaps this only matters to accountants. (The Simpsons Archive's Brian Petersen notes that codes would be assigned when the contracts were made, and possibly these four were intended for a special use, like home video or a summer season neither 7 nor 8; eventually they did become regular episodes in the regular schedule, even if 3G03 did have a special Friday premiere, but the codes wouldn't change.)
• Most of season 9 (5F01-22) was executive produced by Mike Scully, but 5F23 and 5F24 (clip show #4) were done by David Mirkin instead. They also aired near the beginning of the season, further cementing their role as "outside" episodes, even though the numbering was finally contiguous. It's possible that numbers like 5F31 and 5F32 were proposed but rejected. Anyhow, because of both producer and air order, it seems reasonable to consider 5F22 the main end of production season 9, as well as the 2-character prefix era (though see 9ABF notes below), meaning that distinction need not be granted to "a cheesy clip show!"

The two music videos from season 2 have codes 7F75 ("Do the Bartman") and 7F76 ("Deep, Deep Trouble"), although these do not appear onscreen even in the end credits. These are official (seen on slates provided to broadcasters but not meant to be broadcast); the 7F corresponds to season 2, and the choice of number seems to be, essentially, high enough to indicate them as special non-episode productions. More arbitrarily high numbers will be seen in other 20thCFT productions in this document.

Morgan Spurlock's documentary special, not considered an episode, gets a Simpsons-associated production code, too, the credits reading "THE SIMPSONS 20TH ANNIVERSARY SPECIAL IN 3-D! ON ICE!" (minus the colon usually seen after "special"), then "EPISODE LABF21" (no "#"). This aired a few weeks after the 20th anniversary of the series, following episode LABF20 (the maximum code in a short production season). It's a little odd to have the number contiguous, but that's what it says. Note it is twice the length of one episode.

The original Simpsons shorts from The Tracey Ullman Show are listed, for example here, with codes MG01-48 (MG=Matt Groening), though they do not appear onscreen. They're not 20thCFT codes, of course. These seem to be official even if the precise format may not be; they are separate from air order and production order of the Ullman episodes they were included in (see 4W/5W codes and dates in that list), and, more solidly, a sample storyboard seen in the Icons Unearthed documentary series about The Simpsons corroborates the use of MG22 for "The Pagans", with a "22" penciled in after "Matt Groening no." in the template. Yes, it's the 22nd aired as well, but even at Klasky-Csupo they had to keep the shorts straight just as one would need to keep full episodes straight during production.

According to Brian Petersen and his sources, production season 9 used 5F and 9ABF in different places; "9ABFxx numbers began appearing on various internal documents right away, such as music cue sheets." 5F codes appear in the credits and seem most official; Brian speculates that it's "maybe because when all their scripts were originally written and printed, the 5F## numbers still hadn't yet been 'recalled' by 20thCFT" and notes that the first episode pinned with the alternate designation was 5F05 (9ABF05). Various shows during that 97-98 season did begin adopting the new system in onscreen codes at different points, as seen below.

Recent episodes in syndication, etc. (season 34 up?), have added a separate episode code to the non-English dub credits that have been inserted in those copies since about season 19. These include, for example, the Spanish title of the episode, as well as the standard production code, then the new alternative code, e.g., "E0732" for UABF21, apparently indicating a cumulative air order sequence. But that is episode 731 to air (counting WABF04/WABF05 as two), so why is it off by one? Then it gets weirder. Season 34 (episodes 729-750 to air) is given as E0730-E0751 in air order. Season 35 (episodes 751-768 to air) is E0752-E0769, but in production order of just that season, not saving a spot for 35ABF08! This all highlights the problem with such a system: it depends on too many factors, does not agree with the general consensus, doesn't appear on original broadcasts... it's nice, including allowing room for over a thousand episodes, but doesn't help outside a small range of use, and now with season 35 it doesn't even have internal consistency.

Most of the notes above benefit from the perspective of history, but shifting code systems did cause confusion at the time. Many old episode capsules on this site refer to strange entities such as [8[FG]01], reflecting the strange progression from 7G to 7F to 8F with no clear pattern. There may have been anticipation that a renumbering would occur, making the 8Fs into 8Gs or something. The notation is used for the 7Gs and 7Fs too, which is actually more confusing because a single reference could mean either of two episodes. The internal brackets, around "FG", may be an application of regular expressions. (The outer brackets are not really part of the codes but some people seemed to like them to set codes apart; they are seen often in documents here, newsgroup posts, etc., but have dwindled in usage.)
Because all but 17 episodes through the FABF series used nothing but digits and letters A to F, especially once the new ABF codes came about, they bore a superficial resemblance to hexadecimal notation (base-16 as used in computing), but of course that is just a coincidence, with the series letter being early in the alphabet just as the AB_ portion of the sequence is.

Production code references in the show

Even before the writers of The Simpsons knew how rabid fans would make use of the cryptic production codes, those codes began flavoring the show. Some notable examples (other good ones I've missed are welcome):

• Sector 7G at the Springfield Nuclear Power Plant owes its name to the randomly assigned code prefix for season 1. (Claims that it's the other way around require ignoring the way codes were assigned, or at least the very early cajoling of 20thCFT by a knowledgeable producer: "Hey, I know we're going to get a number-letter code, and the boys really like 7G for Homer's workspace in episode 10. Is that available?")
• Episode codes are often used within their own episodes when a similar string of letters and numbers is needed; a famous early example is the prisoner number of the character who'd come to be known as Snake, first introduced in 7F20 with that code on his uniform, and persisting through many appearances. Some one-off examples are in the Meta References page.
• In 4F12, in a scene poking fun at obsessive nerds, a flaw is indicated in Itchy & Scratchy episode "2F09". Note that Simpsons episode 2F09 actually has no I&S cartoon. The code "4F12" is also seen on an animation cel for Poochie's final episode, another example of the point above.
• During a Xena: Warrior Princess panel in BABF01, Frink pesters Lucy Lawless about continuity errors in her show, referring to made-up episode codes "BF12" and "AG4". Though these do not follow any code style, it's worth noting the similarity to the BABF codes this episode ushered in.
• In DABF15, Lisa's professor introduces Itchy & Scratchy episode "DABF06" (pausing oddly before the F) in a scholarly context; Simpsons DABF06 earlier in the season does have an I&S installment, though not the same one.
• In OABF06, Ned tells Marge that he was once Bart's teacher, seeming to cite an episode code before elaborating and keeping it a plausible non-self-aware statement: "You can look it up: CADF12. Those were his grades and the days he was absent. CADF12." This is extremely close to a modern Simpsons code, except for the D; B is still a grade, but perhaps makes too high an average for Bart, and anyway, keeping it fictional avoids needing to find a real episode that supports the claim. The enunciation is pretty good, though the second time it's full of little pauses.

General history and the phases of 20thCFT production codes

This is a general history of 20th Century Fox Television production codes, showing a gradual evolution through over 65 years and counting. For almost six decades, nearly all of these shows have put their production codes in the credits, allowing for direct examination without reliance on external sources. It's useful to see how Simpsons codes fit in (a show airing for over half of the period of onscreen codes!), or those of your favorite shows, but fascinating all on its own.

These are shows for which 20th is the production company, and that is not equivalent to airing on the Fox network. The company name has changed over the years, along with the official name on copyrights, end logos, etc., particularly after the Disney buyout, resulting in "20th Television" branding around 2020. Since this history is almost exclusively pre-Disney, the old name makes the most sense here, along with abbreviations like "20thCFT" or just "20th". (Other names seen in credits and logos include Twentieth Century–Fox Film Corporation [alternatively with a hyphen or just a space between Century and Fox], 20th Television Animation, etc.) Onscreen codes are sometimes found elsewhere in the television landscape; notably, most Fox-related companies include them, and some are discussed later.

Sources, formatting, etc.

Brian Petersen of The Simpsons Archive is responsible for several dozen shows' worth of code information that seeded this project, along with other useful information and pointers. Episode lists at sites such as epguides.com, tv.com, and defunct feeder sites (as seen via Wayback Machine), plus Wikipedia, were good resources. Direct confirmation of many entries is due to some diligent TV viewing and the wide availability of home video releases, and unofficial Youtube archives of nearly forgotten shows. Special thanks to obsessive uploaders of split-screen and text credits meant to archive network/news promos! (One source I do not have is anything official at 20thCFT, though getting some historical inside information from production archives, studio memos, etc. would be great.)

In most of the grids and lists below, codes I have personally witnessed in a real broadcast, archive, or home video release are in bold (with hyphenation style to match); those I have seen the absence of are in italics. Some of these are full season confirmations, others a handful of episodes. Codes not in bold are unconfirmed (series not available to view, in most older cases, or not a priority) and may only be known from scripts and the like (particularly LOC records such as those Brian examined). It is possible that some shows' credits and code styles were modified between broadcast and home video release, though most display the odd mixture one would expect to be the very target of such revisions.

Years are frequently listed as 2-digit abbreviations, e.g., 96 for 1996; stylistically they should have an apostrophe ('96 or really ’96) but there are so many it would get messy. There should be no confusion over what century is meant, with dates ranging only from 1956 to the 2020s.

Since nearly all shows listed used the last two characters to represent an in-season episode number, I omit these and compare only the prefixes, apart from pilots and other singletons. Seasons are organized by traditional fall-to-spring calendar years, with midseason series and other oddities fit in as best possible. Holdover episodes (those not aired until the next broadcast season) are generally irrelevant here. Most wording and punctuation choices are generalized, too, with some series simply including codes, some using "#" or "No.", along with "Production" and so on. Combined multi-part episodes, which usually have two or more separate production codes (pilots being the main exception), tend to chain the codes together in full or without repetition of the prefix, joined by a slash, ampersand, the word "and"...; some notable examples are provided.

Tables are listed in premiere order. Footnotes under tables list out minor details and exceptions, even though half this document's content is essentially a footnote.

A note on pilots and TV movies

A pilot is a demonstration of what a TV series would be like, often in the style of a full or even double-length episode. It is used to sell the series and gauge interest with executives, focus groups, or the public to determine what series to pick up. Not all series have pilots (e.g., those whose appeal or style is already evident), and some are never broadcast; some may be short demo reels, some may have been retooled or recast enough that they don't match the final series. Other series run their pilots as their first episodes, possibly with some small changes, new credit sequences, etc., or do use them later in the season after some episodes that may hook audiences more quickly. In other cases, footage from an otherwise unusable pilot may be salvaged and integrated into a new episode (Star Trek's "The Menagerie" is a famous example). A "backdoor" pilot is an episode of an existing series that introduces new characters in the hope of generating interest in a spinoff. Production codes for pilots often have a special number or pattern, and those will be discussed in each era.

The pilot is not equivalent to or a synonym for the first episode of a series, although when the pilot or a mildly changed version is broadcast, it frequently is titled "Pilot" or the name of the series, so you're probably safe then. Animated shows seem more likely to have short presentation reels, about the length of one act, because of the expense of animation; for The Simpsons the Ullman shorts likely served this purpose, and calling any season 1 episode a pilot would be wrong. (Futurama's "Space Pilot 3000" and "Episode Two: The Series Has Landed" seem to be a joke about the usual live-action practice, not a real example of it.)

Unsuccessful pilots may be broadcast before or after the decision not to pick up their series. Some are aired to gauge viewer interest and may be branded as specials or (for suitably long double episodes) TV movies; if they already failed to get picked up, they may also run as TV movies to not be a total loss. This blurs the line between failed pilots and productions truly designed as TV movies (with no intent to start a series). In the grids and lists below, I've tried to figure out which is which, but I may call a failed pilot a TVM or special, or vice versa. The "season" such a production belongs to can be fuzzy too.

Unsuccessful and unaired pilots and demos of all types are often released as bonus features on DVD, etc., for example, with their successful series, or with theatrical movies they were meant to spin off from or old series they were attempting to reboot. Several codes here were garnered from these.

The 60s: 2-digit prefixes and the birth of onscreen codes

For the early days of 20thCFT, I can find only one set of reported production codes: the second season of Broken Arrow (56-58), 4-34 to 4-72, for episodes 34 to 72 of the series, apparently their 4th.

After that, we see four-digit episode numbers, with a two-digit prefix indicating the series/season (not able to be broken down further) and the usual in-season episode number after that. There are patterns here: for the most part, the second digit tended to remain the same for a series while the first was incremented by year, and even that first digit has a vague correlation to the calendar year. However, for most of the decade, these production codes were not shown onscreen.

Suddenly, across the board, in November 1966 codes began to appear in the end credits, typically stuck in near the bottom of the copyright page. Someone at the studio must have declared a new policy, for at least ten series rolled them out in the span of a month and I've found no holdouts. Some episodes with lower production codes yet to air remained code-free, some put the codes in, each series varying in its treatment, presumably based on the degree of production completion and ability to get it done. In this half season, it also took a few episodes for many series to integrate the codes into their usual credits style, with many early ones missing drop shadows, experimenting with layout and size, even making alignment and font/style errors. (In the grid below, bold prefixes for this season carry an implication of a partial season of unseen codes.)

In this period, codes were usually unadorned: mystery numbers hanging around at the bottom of the screen, maybe with a "#" in front as the decade went on. Multi-part episodes (each part aired on a different night) usually listed one numeric code shared between parts with a part-number suffix, skipping an adjacent number entirely, but there was no common system for this, and examples are listed below. This practice seems confined to the 60s.

Separately-numbered pilots were drawn from a special sequence. Besides the reported 3303 for Five Fingers in 1959, a sequence beginning with 60, then 62 (and maybe 63), supplied pilot codes; this helped avoid wasting a prefix for a series that never got picked up, and once it did, if the pilot aired, the "01" episode number was skipped (see "01+", "02+" notes, etc.). At least two series list two pilot codes in their aired single-length premieres, suggesting a few attempts to shape them or perhaps a merging of two concepts. Some series, especially before onscreen codes, may have had separate pilot numbers not found in the grid.

Additional code numbers and oddities

• Special effects 2nd unit footage for the last three (color) seasons of Voyage to the Bottom of the Sea is included as a DVD extra, and its slates show the codes 8297, 9297, and 1394. This very nicely confirms the 82 prefix but also gives another good example of arbitrarily high non-episode production codes. Similarly, test special effects footage from the same producers' The Time Tunnel included on DVD has a slate number of 9697 (suggesting it was done after the series had been picked up).
• Voyage to the Bottom of the Sea also provides one of the strangest code placements I've ever seen on DVD packaging. Official Fox DVDs of the first three seasons through 2007, on double-sided discs with only a thin circular strip of text as a label, indicated episode ranges per side, in cumulative order, ending in episode 84. The 2009 DVDs of season 4, volume 1 used the production codes! For example, "episodes 1301,1306". These also included "6008" for what is called the re-cut unaired pilot (in color), and apart from that one side the hubs' use of numerical order conflicts with air order, so the codes are slightly wrong in addition to being, I'm sure, utterly befuddling to most of the DVD owners. The printed box art/inserts include many episode details, but not these codes. And the final volume, in 2010, goes a third way, listing episodes 14-26 (of season 4). Little wonder. I've seen 2-digit episode codes on geek-friendly Star Trek menus alongside titles; I've seen codes in production order on Rhino's old MST3K DVD boxes, etc.; are Voyage fans nerdy enough to appreciate this? (By the way, its first episode is variously reported as 6008 and 7001; could it be that 6008 is the color pilot, and then the B&W first episode got a new code, possibly 7001 or even a misread 7201?)
• Batman onscreen codes are already odd (literally), as noted below, with a variety of multi-part numbering systems, but after the half season of inclusion in the credits, they are completely absent for season 3! Why? Apart from Journey to the Unknown, which was only distributed by 20th, all other series of the time seemed to include codes. (See also 80s!)
• Peyton Place goes its own way after playing along with the onscreen code style for a while; see footnote below.
• Several series are missing episode codes, suggesting they were abandoned during production, possibly with new codes at the end of the sequence added in. These early examples include (or don't include) Five Fingers 3715, Adventures in Paradise 3505, and Voyage... 8208. Skipped codes become less frequent as the decades go on; my hunch is that later episodes in a production run are moved down to fill a gap.

	59 -60	60 -61	61 -62	62 -63	63 -64	64 -65	65 -66	66 -67	67 -68	68 -69	69 -70	Notes
The Many Loves of Dobie Gillis (Dobie Gillis)	34	44	54	64								01+; see also 5T79
Five Fingers	3303 37											02+
Adventures in Paradise	35	45	55									01+
Hong Kong		41										01+
Bus Stop			53
Margie			57
Voyage to the Bottom of the Sea						6008 72	82	92	13			02+; pilot also listed as 7001
Peyton Place						??	??	90 91	22 ###*	###*		### = episode # (397-514)*
Valentine's Day						6010 75
12 O'Clock High						6011 73	83	93				02+?; 2-parter 7329 on both?
Daniel Boone						6013 74*	84*	94*	14	30	50	02+; 2-parters vary*
Lost in Space							85	95	15			01+
The Long, Hot Summer							20
The Loner							21					01+; 2122-A/B
Batman							6028 87	97	17		03+; S1/2 odd #s; "-I"/II+"-PT. 1"/2/3*
Blue Light							6026 88					02+
The Monroes								6031 81				02+
The Tammy Grimes Show								11
The Green Hornet								98				01+; "-PT. 1"/2*
The Time Tunnel								6034 96				02+
The Felony Squad								89	19	29		2-parters vary*
Custer									6045- 6050 25			"#6045-6050" dual pilot #; 02+
Judd for the Defense									6044& 6012 18	28		"6044 & 6012" dual pilot #; may use -1/2
Julia										6203 38	48	02+; "part i"/ii E-3 (see below)*
The Ghost & Mrs. Muir										6205 32	52	02+
Land of the Giants										24	47	01+
Lancer										6208 31	51	02+; older pilot blurry (6006?)
Journey to the Unknown										39		01+; 20th distr.
Room 222											6215 49	02+; 4 more (see below)
Bracken's World											6318 58	Or 6216?*; 02+?; E-2 (see below)
Nanny and the Professor											6221 59	02+; E-4, F-4 (see below)

Table 1: All-numeric codes (up to 69-70).
*Peyton Place was a prime-time soap opera, airing 2 or sometimes 3 times a week (just weekly in the final few months) and never taking a break, with 514 episodes over nearly 5 years! Like every other show I've found, it began displaying 4-digit codes in the credits in late 1966, but because it didn't have typical production seasons, and did often have over 100 episodes per year, the numbering systems didn't quite fit it. I have no idea whether earlier episodes had official 20thCFT numbers or what they'd be (maybe a 7_01-99 and 8_00-99); perhaps a memo went out that all shows needed codes onscreen and these numbers began getting assigned right here (though in that case I'd expect an 01 or 22ish). Anyhow, episode 289 (11/23/66) was 9089, 9099 gave way to 9100, and as September 1967 and the start of a new broadcast season rolled around, 9167 led to 2268 (episode 368, 9/7/67). These three prefixes all fit with other shows'. Yet I guess someone at PP wasn't terribly happy with this system, perhaps not looking forward to getting a prefix to follow 22; before the digits could roll over, 2296 led to simply the sequential episode number (397, 12/25/67), which remained in that spot through the finale (514) in June 1969.
*Daniel Boone's season 1 two-part episode has 7426 listed for both parts, and one in season 2 gets separate codes of 8429 and 8430, but none of these are onscreen. In season 3, a two-parter is "9416-PT1" and "9417-PT2", having both separate numbers and part designations.
*Batman is wild. Seasons 1 and 2 aired twice weekly with 2- and sometimes 3-parters, and that's probably why only odd numbers are used, with part numbers. Season 3 was weekly but had several multi-part episodes, using the same idea (and even numbers, though multi-part episodes are still odds!). It all balanced in the end, with extra parts causing some sequence gaps rather than lower maxima. When codes started appearing onscreen, they were "-I" and "-II" for three pairs (9725, 9727, 9729) and then "-PT. 1" and "-PT. 2" (and 3) thereafter (even on the late-airing 9715). Inexplicably, as noted above, season 3 seems to have dropped onscreen codes entirely!
*The Green Hornet has several two-parters, though one was before codes were shown, the others using "9818-PT. 1" and "2" (and 9825), skipping 9819 and 9826, like Batman. Some guides just list them as 9818/19/25/26.
*The Felony Squad I could only find a few episodes of, enough to spot at least an "8921 PT 1" in season 1 and "1913" on its own for part of a two-parter in season 2, suggesting it may have stopped that notation. I can't confirm or deny a separate pilot code.
*Julia has one two-parter listed onscreen as "#4827 part i" and "ii" (lots of space after the episode number, lowercase like the rest of the credits) and no 4826, though some guides list them as 4826 and 4827.
*It's hard to make out the code on the Bracken's World pilot in the copies I've found, and I don't see it documented anywhere. Second digit might be 2, fourth might be 6, or I might be further off. Better info is welcome!

The 70s: random letters and numbers

The numbers were not going to hold out forever. By the end of the decade, over half of the available prefixes appeared. For the 70-71 season, existing and new shows alike would feature a prefix with a letter and one digit instead. This was orderly at first: that season's letter was E, perhaps to evoke the word "episode" (see notes on confusion below). Then F. G would usually follow, but a random letter order that I cannot explain took over. Most seasons did have one or two letters for full season prefixes, with numbers assigned haphazardly (renewed shows didn't retain a semi-consistent number); though there is some broad order as seen from a distance, rote memorization is all one can rely on for tracking a series across multiple seasons. If you thought 1F and 3F was hard, you don't want to try to remember M*A*S*H codes. Through the 90s, the main letters not seen in prefixes are I, O, and Q; U is consistently used, and other exceptions may just be undiscovered and not forbidden.

Pilot codes varied. One remnant of the 6x sequence is the failed pilot They Call It Murder (6701), which did not air until 71 but was produced in 69-70, perhaps while the the sequence was still moving along. But for the bulk of the decade, pilots, TVMs, and other presentations got one of two things: Z-#### (four digits with no apparent pattern) and a letter-number prefix dedicated just for this purpose (e.g., R-9##, which has surfaced more than once). Most but not all of the latter use the digit 9, and I assume there were dozens of pilots that never made it but drew from these sequences. Most of the "episode" numbers are low, but examples go as high as 10, and the two failed pilots from 76 show the prefixes did get repeated. Only a few of those codes don't use 9, and 9 is rarely (if ever!) used in regular prefixes. (Hagen is the main exception here and I've yet to confirm its partially reported codes!) By the middle of the decade, skipping the "01" episode no longer occurred, whether there was a separate pilot code or not.

For the 70s and early 80s, codes migrated a little higher on the screen but still generally occupied a space of their own, not explaining their role. With rare exceptions, these new codes contained a hyphen (or dash, if you like) between the letter and the digit of the prefix, probably to set apart the character sets, yet resulting in an apparent but meaningless three-digit number (better than an apparent but meaningless four-digit number?). As with every single other evolution of code styles, it caused some confusion for both producers and viewers. The first episode of Room 222's season 2, though not the first to air, was listed as #E501 (the only "#" in 5 seasons); similarly Bracken's World had what looks like "E#201" before finding the hyphenated style. Whether "E" came from "episode" or not, it surely could be taken that way (at least for Bracken it did work as "episode 201"!), and between the inaugural "E" season and the separating hyphen, it paved the way for fan guides to omit the letter entirely (even in 2009 I had only the numbers for Room 222). Occasional shows dropped the hyphen or replaced it with a space throughout the decade, sometimes just for an episode or two! (Confusion between "0" and "O" also reared its head sometimes, as in The Paper Chase's pilot that appears to say "X-91O", but maybe it's an aesthetic choice. Yet more than once, into the 90s, I've seen O1 to O9, then 10, 20, etc. and 01-09 on subsequent seasons. I am not reporting these as a general rule.)

Oddities

• M*A*S*H offers a variety of double-length two-part episode code styles, though mostly they are variations in punctuation: U-801 — U-802, Y-101 Y-102, Z-419-Z-420.
  On DVD at least, one is shown just as G-504 (without mentioning its second half, G-506); T-408 and T-409 survive only as divided syndication edits and list just one code on DVD no matter which viewing option is selected (and it appears to always be 08 but it's too blurry to tell)!
  Curiously, the massive grand finale, 9-B04 (a preview of 80s style for you), is about five times the length of a single episode, with an episode number from the middle of the sequence, yet just has that single code.

68 -70

70 -71

71 -72

72 -73

73 -74

74 -75

75 -76

76 -77

77 -78

78 -79

79 -80

80 -81

Notes

Julia

6203 38 48

E-3

Room 222

6215 49

E-5

F-2

J-1

K-3

"#E501", "E-502"+

Bracken's World

6318 58

E-2

"E#201", "E-202"+

Nanny/the Professor

6221 59

E-4

F-4

Arnie

E-1

F-3

01+?

Cade's County

F-1

01+; "F124"*

Mr and Mrs Bo Jo Jones

F801

TVM Nov. 71

They Call It Murder

6701

Pilot prod. 69-70, aired Dec. 71

Anna and the King

H-901 J-2

02+

M*A*S*H

Z-9522 J-3*

K-4

B-3

G-5

U-8

Y-1

T-4

S-6

Z-4

02+?; 1-G, 9-B (see below)

The New Perry Mason

K-1

01+

Roll Out!

K-7

Pilot no code?

Planet of the Apes

B-5

01+

The Mark of Zorro

C-901

TVM Oct. 74

Karen

D-9

01?

Swiss Family Robinson

G-201 M7

01+; closer to "M 7"

Time Travelers

R-903

Pilot Mar. 76

State Fair

R-904

Pilot May 76

That's Hollywood

U-3

T-1*

1K (see below)

James at 15 (James at 16*)

Z-2978 Y-4

01+; "Y 408", "Y 402" +?

The Paper Chase

X-910 T-7

01+; cont. 80s (see below)

Trapper John, M.D.

A-910 V-4

Z-5

01+; 5 more (see below)

Swan Song

S-901

TVM Feb. 80?

Hagen

S-401 ?-9*

01+

Breaking Away

Z-902 Z-6

01+

Table 2: Letter-number codes (70-81) and overlaps in both directions for convenience.
*Cade's County has at least one code presented with no hyphen, and may have some with a space. It also has at least one two-parter compilation, whose parts I suspect but cannot yet confirm had regular F-1 codes, aired as a TVM: "Slay Ride" (Z-9523?), with others seeming to have no onscreen codes at all. The long Z code fits with other special presentations, but I'd love to get more info on all of this.
*The first episode of M*A*S*H has this Z pilot code on DVD, though some guides list it as J-301. I'm going by the only screen evidence I have.
*That's Hollywood has been hard to find much information about at all, such as episode list or airdates, let alone codes. There seem to be just three production seasons, though. The few early episodes I've been able to find do not seem to have onscreen codes, but I'm not sure whether they're U-3 or T-1 (both, I think). I have seen some onscreen 1Ks.
*James at 15 became James at 16 halfway through the season, crossing out the old age in the title sequence, and this change goes with air order, not production order. By the way, a previously-reported "905" pilot code I saw in a guide seems to be based only on its airdate!
*Hagen guides list the pilot as S-401 and the rest as 9__ (including a 901). I assume the letter was ignored there, as it was in guides for many shows around this time.

The 80s: random numbers and letters

Starting in 81-82, there was another change: the prefix became digit-letter, not letter-digit. This, in some form, has been the basis for all main sequence codes since. The randomness continues, with a vague association of a digit to a season, but even looser than the letter-season combinations of the 70s. After starting off nicely with 1, it seems to go backwards for a season, dabbling in 9, 8, and even 7, then proceeding loosely through 2-7. Letters are utterly inconsistent, even more random than the digits of the 70s, and it was the rare show indeed that kept the same letter through even two seasons (The Tracey Ullman Show may be the only no-change series, though Anything but Love's letter was consistent through this period). Of course, it is at the end of this period that The Simpsons got its 7G.

However, for some reason, several shows did not include production codes in their credits (through the early 90s). These are all 20thCFT shows, as far as I can tell, and although some exceptions to the code patterns described have existed, shows with regular codes generally did display them. If there is a common trait to those without onscreen codes, I am not sure of it, although it seems most or all of the shows in question were taped and not filmed, so perhaps a different postproduction unit was in charge. I'd love to figure this out.

Pilots changed several times, too. I see three last examples of entirely separate pilot codes for 83-84, two of them with a 9C prefix (compare the use of 9 in 70s pilot codes). In mid-84, there is a TVM, Love Thy Neighbor, with code 3K99, and a failed pilot for yet another M*A*S*H spinoff, W*A*L*T*E*R, whose code is hard to read (and in parentheses!) but might be 3A99, or 2A99, or another high episode number. This is likely a move toward the long-lived practice of devoting a whole prefix to a series right away with a certain special pilot episode number.

As early as 85-86, or 86-87 with better "really a pilot" evidence, TVMs and pilots began getting their own prefixes and using episode number 79. This special number stayed in use for nearly 30 years (or maybe longer)! It also found its way into other Fox-related systems. Why 79? Apparently 99 was no good, and this was just right: high enough to be out of the way, low enough to leave some very high numbers reserved (perhaps for more internal stuff like Voyage to the Bottom of the Sea 2nd unit). Maybe it was a misread 99 and it stuck. It seems unlikely to be a reference to the year, or an homage to the number of original Star Trek episodes or anything. Many 79s were aired as episodes, and at least a few became reworked into 01s (see Dollhouse for example), but the general rule from this point on is that new episodes start from 01, so a typical 22-episode season might be 79 and 01-21. As usual, some series just began with 01, including some that called the 01 (or 01 and 02) the pilot.

Later in the decade, the codes began migrating into blurbs of legalese as little afterthoughts, hanging out next to an "all rights reserved" or "Twentieth Century Fox Film Corporation"; some stayed in their own space but added "Prod." or something similar.

Under this system, the hyphenation began to drop out. It's not a surprise; 1-E01 means just as much as E-301 (which is not the three hundred first of anything or third of something/first of something else), but why mix letters and numbers on one side while separating them on the other? There's no pattern to this, but just as many little exceptions. Partway through its first number-letter season, M*A*S*H switched to the more logically separated "1G-11" through "1G-24", but then back to "9-B" the next year, mixed with "1G-" holdovers! The last hyphenated codes I've seen are on Heart of the City (86-87), and yet the practice remained in the industry for years after that: I have seen a 1997 Simpsons syndication schedule meant for TV stations that lists episodes as old as "7-G12" and as new as "3-F16", despite the total lack of hyphens in this show's codes. Brian's feeling is that either hyphens persisted officially through the 90s but gradually got dropped by producers, or they were dropped at the start of the 80s but well-meaning producers, schedulers, etc. kept reinserting them, assuming their omission was a mistake. In some places, old habits die hard.

Additional code numbers and oddities

• The Fall Guy uses only odd episode numbers for its first two seasons; its double-length premiere is just 1-E01, and then the rest are 1-E03, 05, etc. Some pilots/premieres of that length take up an 01 and 02 (listed or not), which would explain starting from 03, but this is puzzling. Also, an illustrative case of ambiguity is seen in syndication, where the halves of the first episode are both listed as 1-E01 (part 2 uses the original card but part 1's is from 1986 with two copyright dates and 86 design).
• At least one Tracey Ullman Show special has an arbitrarily high episode code, which I think is 5W75 (it's hard to make out).
• Several 80s episodes of The Paper Chase seem to be confused about their codes, at least on DVD (noted for relying at times on secondary/syndication sources), some swapped or doubled up, 4M01 missing a code entirely, but it's possible they were originally broadcast correctly. The double-length grand finale uses the most compact designation "4M05/6".
• In the whole decade, the only skipped episode code I've spotted is 9 to 5's 2C08; that series also combines its last two seasons' codes as 4V01-26 and 4X27-52.
• The pilot for The Highwayman has 20thCFT code 5L79, but the rest of the series uses a different code system because it was picked up as a series by a different company.

	70s	81 -82	82 -83	83 -84	84 -85	85 -86	86 -87	87 -88	88 -89	89 -90	Notes
M*A*S*H	^	1-G 1G-	9-B								"1-G01" to "1-G10", "1G-11" to "1G-24"
That's Hollywood	^	1K
The Paper Chase	^		8-C*	2V*	3M*	4M*
Trapper John, M.D.	^	1-M	8-B	2-F	3-L	4-J
The Fall Guy		1-E	7-B	2-G	2-Z	4-E					01+; S1/2 odd #s only
9 to 5		1U*	2-C	1S			4V	4X			01+; 4V01-26, 4X27-52
Trauma Center				?? 2-H							Pilot code unknown; 01+; "2H07"
AfterMASH				2-E	2-W						01+
Emerald Point N.A.S.				2-K							"2-K01/02" on pilot
Manimal				3-D01 2-L*							01+
Automan				9-C09 2-M*							01+
Masquerade				9C-03 2-J							01+; "2J03" on first aired of 2Js
Love Thy Neighbor					3K99						TVM 5/23/84
W*A*L*T*E*R					3A99?						"(3A99)"/2A? 7/17/84*
Cover Up					3-J					"3J01/2" pilot, "3J13"
Mr. Belvedere					3T	4G	5A	5M	5V	6V	01+
Half Nelson					3U						01+
Charlie & Co.						6S					79/01+
A Letter to Three Wives						3-N79					TVM 12/16/85
Fathers and Sons						6U
The Wizard							4P				79/01+
L.A. Law							4L	5K	7A	7D	01+*; #L (see below)
Heart of the City							4-S				79/01+
The Tracey Ullman Show							4W* / 5W*			7W	01+
The Highwayman								5L79			8801+ non-20th series
Hooperman								5J	6X		01+
Second Chance/Boys Will Be Boys								??*
Leg Work								5G			79/01+
Bring Me the Head of Dobie Gillis								5T79			TVM Feb. 88*
Anything but Love									5Y	6Y	01+; #X (see below)
Have Faith									5R		79/01+
Sister Kate										5Z	01+
Alien Nation										6W	79/01+; see also 1N79
The Simpsons										7G	01+; #F+ (see below)
In Living Color										7H	01+; #U (see below)

Table 3: Random number-letter codes (81-90), no overlaps. (^=see 70s.)
*The last four seasons of The Paper Chase aired mostly in spring-summer runs from 83 to 86; I filed them this way. Note also that guides and DVDs call both 8-C and 2V season 2 and title cards say "the second year", but looking at airdates and production codes I say they're separate.
*The single example of a season 1 9 to 5 code I've been able to see is a bit muddy; it looks like "1 U01" with a small space, but I can't entirely rule out a hyphen.
*Manimal and Automan are hourlong shows with 90-minute pilots. I'm not listing every extra-length pilot but clarifying an earlier version of this list noting my confusion since I wasn't sure whether I was looking at pilot/series or TVM/spinoff.
*W*A*L*T*E*R (pilot): see description above.
*L.A. Law uses 4L01 for its double-length pilot and 4L03+ for the rest of season 1, suggesting the pilot's second half may be counted as 4L02.
*The Tracey Ullman Show is kind of odd; the 4W and 5W seasons, as marked, correspond to the calendar seasons they began, but two production seasons were stretched into three air seasons, and 7W is the third production season and 4th year/air season. The numbering might reflect an attempt to keep order by skipping an unproduced 6W season, or maybe Alien Nation had already scooped up that code.
*Second Chance and Boys Will Be Boys, two shows resulting from severe retooling midseason to cancel one but retain star Matthew Perry, make up a single broadcast season with seamless coding, but no onscreen codes and no help from the net leave me stumped. Maybe they had 5_ or 4_ codes, maybe nothing of the kind, but I'd still like to list it.
*Bring Me the Head of Dobie Gillis is the second followup to the series, and may have been meant as a TVM or pilot for a reboot, airing in February 88. The first followup, Whatever Happened to Dobie Gillis?, was a failed pilot for a reboot, airing in May 77, and not only can I not find a code for it, it may be lost.

The 90s: meaningful numbers and letters

Finally, by the 90-91 season, there was an across-the-board attempt to standardize codes. The digit-letter prefix was still used, but now each digit represented a split calendar year for the broadcast season, and each letter represented one series consistently. It seems possible, based on proliferation of examples, that some letters were chosen or requested purposefully for this system. (After 7-9, digits wrapped around to 1-5; 0 was skipped, and 6 never had a chance to be part of this system.) Pilots almost entirely used the 79 episode numbers (when applicable).

Shows carried over from the 80s, at least those I know of, were assigned new letters, mostly because the bulk of them had 7_ codes in 89-90 and 7 was the digit for 90-91! I suspect that, with the risk of overlapping codes between the 80s and 90s versions (hyphens or not), 7 was chosen to maximize the amount of available ones for the longest time (it had just been in use but not for many shows, and 8 and 9 were barely used). The first overlaps I see are between 93-94 and early 80s codes; most pertinent to this site are Simpsons 2F and Trapper John 2-F. Any overlaps at all are not ideal, and prevent a 20thCFT-wide claim to uniqueness, but it still worked pretty well.

As was discussed above, The Simpsons got letter F (with a dash of G), moving into its second 20thCFT code system, and nearly breaking it by season 9!

Around this time, more series began to label the codes as "Production (#)" or even "[series name] episode #", but plenty left them in the middle of the screen, perhaps with just a "#".

The only point of confusion seems to be the Simpsons-specific "[FG]" stuff discussed above, and a bit of letter-number misreading. There was a lot of consistency: except for seasons from the 80s, the codes are easy to learn, keep straight, and anticipate. The first digit only identifies the year, not a show's own season, but knowledge of the show's premiere date helps. (Shows begun in 93-94, like The X-Files, do also happen to match season number to that digit.)

Additional code numbers and oddities (see also Simpsons section above)

• Early season DVDs of King of the Hill make extensive use of production codes to refer to episodes, not in the packaging, but in the menus, where episode titles and airdates are accompanied by codes, a list of music selections is indexed by code (and for nerd overload also includes music cue numbers like 2M2 and 3M7), etc. Curiously, the season 3 menus for season 2 holdovers list them as 2ABE even though the in-episode codes are still 5E; see transition notes in the next section and backnumbering under Fox in Flight.
• It took just over two seasons for In Living Color to include codes onscreen, with a little 1/I confusion later (see footnote). Also, episode 8U14 seems to be skipped (dropped for a Michael Jackson special, 8U27, and never produced?), and season 3 included 8U27-30 as specials and clip shows mixed in with normal episodes (which went up to 8U26). In season 4, with a jump in sequence, 9U40-45 were best-of clip shows mixed in with normal episodes.
• Dharma & Greg began its run with AE codes (see transitional hiccup in footnote), rather than 5_ codes. Could it be that the 5_ codes were exhausted during code assignment for this season, and an A_ sequence stopgap was instituted and maybe even the last straw before the new system (below) came about? If I could find AA-AD codes, maybe for failed pilots, that would help.

"21st Century Fox": three letters for a longer-term fix

By the end of the 90s, a problem arose. There would be a "6" year soon, and after that, another "7"? Letters can be changed, but only so many times. 5 may already have been exhausted. The next evolution was bipartite: the absolute year digit would change to a relative season number, and the single-letter series identifier would become a 3-letter one. Existing, continuing shows would have to make a change in production code style. Most shows got their current letter after "AB", so for The Simpsons, ABF. (Buffy the Vampire Slayer is a notable exception, see below.) New shows from then on would use a few remaining "AB_", "AC_", and so forth.

Brian's LOC research has shed some light on "AA_" codes, though it's unclear when these were assigned. They seem to apply to series with 3_ and 4_ prefixes, as if to reserve new three-letter codes in case of renewal. The examples: AAF = Fire Co. 132 (4B, set for 1AAF codes despite being a retooling of a series with 3B prefix), AAK = Picket Fences (ended with 3K), AAN = Relativity (4H). Only one of these letters matches; none of these new codes appear in aired episodes. (See also AAB for The Hughleys in Fox in Flight, that series debuting at this time. Related?)

Even the 5_ and AB_ codes had some conflicts and oddities. Not equivalent are 5K (Nothing Sacred) and 1ABK (That's Life), whose aired episodes overlapped by about a week; neither are 5R (The Visitor) and 1ABR (Getting Personal), which had a few months between their air runs. In fact, according to Brian, The Visitor also has ABV codes; ABR seems unavailable, but by taking ABV it may have stopped Buffy from keeping the letter V!

Onscreen, this system was rolled out in the middle of the 97-98 (5) season, with some series changing code styles suddenly yet at different times in the spring, and others waiting until the new 98-99 production season (see footnotes under Table 4). Some fan guides (and even LOC, e.g., for Buffy) listed "6" codes but all onscreen evidence reflects the new system. Holdover episodes and those aired after episodes with the new codes generally did not get adjusted (e.g., Simpsons 5Fs in air season 10, including after AABFs had begun; ...Pizza Place 5Zs of lower numbers in with 1ABZs of higher numbers).

Just as The Simpsons nearly broke the previous system by running through most available digits, it started off the new one by immediately posing a problem: it was about to begin season 10, well-known as a non-single-digit number. The numeric sequence was extended to the alphabet: 10=A, 11=B, etc., making season 10 start with AABF01. Fans expecting a 6F01 or something similar had to make some sense of this, some interpreting it as AAB-F-01 rather than A-ABF-01; a change a season or two earlier, to an 8ABF or 9ABF, would have made it a little clearer. (See also the note about 9ABF05 and similar internal codes, which did not appear onscreen, above.) But whether the longevity of the series had little or much to do with the forward-thinking decision to switch systems, that switch happened without much time to spare!

It's worth noting that this system does trade one piece of encoded information for another: for the 90s system it was possible to determine broadcast season from a prefix, but not the season of a show (without additional knowledge); now it was the other way around. The new system is also more resilient in adding continuity to series with long hiatuses or revivals, simply picking up where they left off. Family Guy and Futurama survived cancellations without prefix gaps, along with Arrested Development and Last Man Standing, to name a few. King of the Hill is an extreme but triumphant example, with its revival going from DABE to EABE seamlessly after 15 years! On the other hand, some series were revived without using their old three letters, and whether the system was misunderstood or the bureaucrats considered them separate series I can't say. The X-Files and Prison Break come to mind; 24 did a little of each approach (though its new letter trio really stood for basically a new series)!

Some confusion still existed, not just among viewers. It's mostly little things, like the brief omission of the "1" season digit in Dharma & Greg during the switch, or the reintroduction of the hyphen in Titus. And one production house seemed to resent the whole thing (see David E. Kelley section).

For both series codes and alphanumeric season numbers, however, a few letters were off-limits, or at least saved for marginal uses. (Of all the developments in this document, by the way, this was the first I got to observe in real time!) These are I, O, Q, and U, and they seem to be skipped primarily to avoid visual confusion at low resolution or with bad signals. I looks like 1 (and J), O like 0 (and Q=G/O, U=V?). U is a real surprise, especially since it appears in all three previous systems. Series codes only use these in retroactive coding or Kelley shows, as far as I can tell.

And the season numbers skip them, too, or did, until The Simpsons once again broke the system by lasting beyond a previously unthinkable 31 seasons! What comes after Z? QUO, of course (and then a resigned flip to 2-digit season numbers). They weren't so forbidden after all! See Simpsons history above for more details. Anyhow, that makes the Simpsons alphabet ABCDEFGHJKLMNPRSTVWXYZQUO (no I). Not the most intuitive, even compared to an abridged but orderly alphabet. It gets worse: for reasons beyond me, Family Guy (the second show to get this far) skipped G, while American Dad! (third) did not! One needs to know the specific show's code history to interpret a season letter now. See above for FG future code speculation.

While the main sequence of A__ codes rolled out like license plates, ticking over about one middle letter per year (a decent way to estimate a show's debut), other 20th-related codes were springing up with similar structure. I haven't explored these as much, but the main set I've found all come from offshoot Fox21: VA_, RA_ and SA_ (only one example of R/S spotted so far), and WA_/WB_ (various years until corporate mergers around 2014). Meanwhile, Fox company recoding and internal coding (see Fox Television Studios and Fox in Flight below) used up a number of Y__, B__, C__, D__ codes, some with letters before numbers instead of between, or so it would seem.

What comes after AZ_? Not BA_, but LA_! This rollover occurred in 2017, and yet, after just a few years, there seems to be a move away from this sequence, or a splintering of sub-companies, perhaps coincidentally timed with the Disney buyout. For 20th Television, I can't believe it: we might be back to random codes after three decades of order, or maybe some very fast movement through the three-letter sequence. Doctor Odyssey in particular could be part of the main L__ sequence at about one middle letter per year, but I have not yet spotted entries linking LB_ and LG_.

Fox Entertainment Studios/Fox Media seems to be keeping onscreen codes but in bare "hotel" style (101, etc.), as with Animal Control and Going Dutch. Bento Box, in its capacity as main production company (under the Fox umbrella since 2019), now uses four-letter series codes (BB plus 2 more), even on some shows otherwise not Fox-branded, but these codes seem to be hand-selected and not in sequence (the first three examples I found happened to be in order!).

For 20th and others, there's a lot more to learn as this develops. Some codes are listed below, and maybe more patterns will emerge.

One more major change and abandonment of longstanding tradition: pilots continued getting 79 episode codes during this three-letter system, even at other Fox studios. But then they seemed to start using plain old 01 instead, even in other Fox companies. The last main sequence 79 I've seen is for The Crazy Ones in 2013, along with a few for some Fox21/FTS series in the next several years. Has 79 been 86ed?

Additional code numbers and oddities

• Several notes for Family Guy:
  • This series has one of the highest contiguously-numbered production seasons, reaching 4ACX35 (vs. a typical contemporary maximum of about 22) for its triumphant 2005 return. (It's true that three of those 35 were originally released as a DVD movie, but they have all aired as single episodes too, and 32 is nothing to sneeze at either.)
  • A special for the "100th" episode, not counting as an episode itself and airing during the tail end of the 5ACX series, got the arbitrarily high episode number 6ACX45. Curiously, a similar "200th" episode special has no apparent code (such as AACX45) and may not have been produced by 20thCFT. A spinoff special, Seth and Alex's Almost Live Comedy Show, received the code 1ARX01, appropriate for its 2009 airing, and may have used that entire ARX identifier all for itself.
  • Poking into skipped-number territory: 7ACX10, "Partial Terms of Endearment", has never aired in the US, though it got a swift DVD release, so it's hardly missing or un-accounted-for, yet looking at a list of airdates and codes one might be confused by its absence.
  • Multi-part episodes have varied in code presentation, but of particular interest here is the crossover episode "The Simpsons Guy", whose full version is listed as "FAMILY GUY EPISODE #BACX22-23".
  • The all-commentary episode "You Can't Handle the Booth!" features a good example of the informal use of simplified production codes: as the family sits down to provide DVD commentary for the underlying episode, a broadcast slate marks it as HACX14 (this episode's own code), but Peter introduces it as 1614 ("sixteen-fourteen").
• Wayward Pines, like The Pretender (see MTM and footnotes), came into the 20th fold during its run, and it received the AZF identifier for season 2 (summer 16, which I am filing under 15-16). Curiously, its first season under FX Productions used YJU101+ codes rather than the usual FX style (something like XWP01001), but that prefix does fit perfectly with Fox in Flight designations for 14-15 FX shows (see below). Maybe its airing on Fox rather than FX is a reason; I have not studied FX codes closely, though.
• 24: Redemption, a special TVM before season 7 and after a gap year, has the code 7AFF50, though its extended version with more cinematic end credits lists no code at all! The later Live Another Day season after season 8 resumed coding with a 9AFF prefix; 24: Legacy with a new cast received the AZK identifier.
• Prison Break's grand finale was 4AKJ22, but a DVD-only double-length "Final Break" released around the same time got designated "4AKJ23 & 4AKJ24", with an unusually fancy "Et"-styled ampersand compared to the typical one seen in other double episodes. Its later Resurrection "event series" got a new identifier, AZM.
• Stacked breaks from form, with its aired pilot being 1AKM78 rather than 79, and picking up at 1AKM02 rather than 01. (An unaired 01 seems unlikely as the DVD set includes several unaired episodes but not one with this number.) The 78 could be a mistake or typo, but it could also be that show's way of handling the new version of the pilot (after an unaired 79) when a role was recast, perhaps even a melding of 79 and 01 (the last part is pure speculation). Most shows seem to keep 79 easily in these cases. See also Method & Red from FTS the previous year, which has a 78 and an 01.
• Two anthology series from Fox21 skipped over season-two codes entirely after those seasons were abandoned in development, so there are no produced 2WAX (American Crime Story, Hurricane Katrina) or 2WBB (Feud, Buckingham Palace) episodes. In the former case, it may have been merely postponed while 3WAX codes were being assigned. Side note on the latter: the second season premiere of Feud (re)uses the title "Pilot", which is a major reach, anthology series or not. (On missing seasons, see also the jump in FTS's The Shield with no production season 6.)
• American Dad! is worth singling out as a series that, like The Simpsons, enjoys using its own production codes as license plates, etc.
• Several season 2 episodes of ...Pizza Place list an (R) after their codes, at least on DVD. Could it stand for revised, repeat, ...? (See also RX codes in WB section.)
• Season 1 of The Simple Life lists episode codes as "The Simple Life Episode 101", etc., in the full-screen DVD credits anyhow (and some aired versions at least). Season 4, the only other one I have been able to sample, uses a more typical style, though typographically suspect, 3AHZ01 and up, leading me to wonder whether the first three air seasons are two production seasons, what 2 and 3 look like, whether any of 1 aired with AHZ codes, etc.
• Previous research for this document turned up AFE codes for The Bernie Mac Show (see Fox Television Studios), which would be right for the date, but it wasn't a 20thCFT series. Or was it going to be, and assigned a code? (Onscreen codes and episode guides all seem to use the FTS system.)
• Purely in the realm of the silly and unofficial, but enlightening: in my 2009 web search for codes, "1ACL01" turned up a fictional epguides.com-style episode guide for 11 seasons of an imaginary spinoff of The Simpsons, The Lovejoys. It was "set" for a 2015 premiere, but the author didn't seem to know that the ACL code indicates that the show'd been in development since 1998. Unfortunately, the projected finale (BACL17/18) was dated 5/15/25, so as of my 2025 update, you've missed the big day in the author's head! Other silly stuff like this is elsewhere on the web, with other imaginary series (such as now-lost ACP examples and most non-Simpsons) using a variety of code styles.

Table 4 (90s codes) is below, and a list of 3-letter code/series assignments follows Table 5. First, there's another transitional matter to discuss.

86 -89

89 -90

90 -91

91 -92

92 -93

93 -94

94 -95

95 -96

96 -97

97 -98

98 -99

99 -00

Notes

L.A. Law

4L 5K 7A

7D

7L

8L

9L

1L

Anything but Love

5Y

6Y

7X

8X

The Simpsons

7G

7F

8F

9F

1F

2F

3F 3G

4F

5F

AABF

BABF

In Living Color

7H

7U

8U*

9U

1U*

Poochinski

7P79

Pilot 7/9/90*

Working It Out

7V

50?/01+*

True Colors

7T

8T

01+*

Babes

7E

79/01+*

Good Grief

7Y

01+

Drexell's Class

8G

01+

Revenge of the Nerds

8N79

Unaired, unsold pilot (91)

Picket Fences

9K

1K

2K

3K

79/01+

Rhythm & Blues

9R

79/01+

The X-Files

1X

2X

3X

4X

5X

6ABX

7ABX

79/01+; see AYW

South Central

1S

79/01+

Wild Oats

2W

79/01+*

Chicago Hope

2M

3M

4M

5M* 4ABM

5ABM

6ABM

79/01+

The 5 Mrs. Buchanans

2B*

79/?

Alien Nation: Dark Horizon

1N79*

The Crew

3W

79/01+

The Preston Episodes

3E

79/01+

Cleghorne!

3L

01+

Space: Above and Beyond

3S

79/01+

L.A. Firefighters (Fire Co. 132)

3B

4B*

99?/02+?

The Pretender

031*

032*

3ABP

4ABP

01+; AER*

Relativity

4H

79/01+

Millennium

4C

5C

3ABC

79/01+

King of the Hill

4E

5E

3ABE

4ABE

01+

Pauly

4P

01+?

Temporarily Yours

4T

01+

Buffy the Vampire Slayer

4V

5V

3ABB

4ABB

01+

Secret Service Guy*

4D

79/01+

413 Hope St.

5W

79/01+

Nothing Sacred

5K

79/01+

The Visitor

5R

79/01+

Dharma & Greg

AE* ABD 1ABD

2ABD

3ABD

79/01+

Two Guys, a Girl, and a Pizza Place (Two Guys and a Girl)

5Z* 1ABZ

2ABZ

3ABZ

79/01+

Table 4: Orderly number-letter codes (90-98) and three-letter codes (98+), with overlaps.
*In Living Color does not show any codes for 2 seasons (and 2 episodes of season 3); the first code seen is 8U03. For most of season 5 the code is typed as IU and I consider this a typographical mistake like 0/O, especially since it was corrected for 1U18 and up, and two earlier episodes (on DVD at least, not sure whether they aired this way, since the credits are in a different style) say "1U 05" and "1U 08".
*Poochinski's 7P code and airdate could place it either at the end of freewheeling 80s era where a lot of 7s were being used or in the first year of the 90s, and its summer airdate does seem to suggest an end-of-season dumping ground over an interest-assessing trial, as does its inclusion on the second Hooperman DVD set and same pedigree, since an 89-90 season would follow that show.
*The pilot of Working It Out does not have the code onscreen, and guides report it as an anomalous 7V50; I have not been able to find other episodes to check out.
*At least one episode of True Colors doesn't have the code onscreen, though most do; the one without seems to be 7T15.
*The pilot of Babes does not have the code (7E79 according to guides) onscreen. Other episodes do.
*Alien Nation (6W, 89-90, see above) ran for just one season, then returned as 5 TV movies from 94 to 97. Only the first of these, Dark Horizon, shows a production code, suggesting to me that it was produced as another double-length pilot for a failed reboot (for 93-94), but spun into a series of TVMs, the rest not assigned codes since they were neither pilots nor episodes (and TVMs went without codes by then?). 1N79 did not air until October 1994, though.
*An unaired 5th episode of Wild Oats seems to be missing the copyright page (and code) entirely.
*Chicago Hope switches format in the middle of season 4. Brian's notes suggest 5M14 to 4ABM15, but epguides.com has 5M15 to 4ABM16. I'd love confirmation, especially from original airings.
*Guides for The 5 Mrs. Buchanans list a 28 prefix, and I'll be darned, it's hard to say from recordings. The aired pilot, which I've seen in both full screen and side text, looks more convincingly like 2B79, and the dozen or so other episodes I was able to view (full screen) could go either way; clearer versions make me lean toward 2B more firmly. And 2+letter is the usual pattern for the year! Is it possible an assigned 2B even got mistyped in the credits as 28? Any inside dirt? (And is there an 01? It seems more likely than not.)
*L.A. Firefighters ran for 6 episodes in summer 96, then was retooled and renamed Fire Co. 132 for a new 4B season which never aired, according to Wikipedia. Its article also lists the pilot as 3B99 (unusual for this period) and suggests no 3B01, but switches between code styles, and I have no broadcasts to check against.
*The Pretender was an MTM production with MTM codes (see that section), then a few episodes into season 2, around the time of corporate mergers, the copyright page started mentioning 20thCFT instead, for part of that season anyhow. Online guides indicate that MTM made season 1 only, yet it's named on the copyright rather than 20th for most of the run, including the TVMs, even after mergers. DVDs use a (later?) Fox logo starting in season 2 and may have other deviations from the original broadcasts, but the codes stay with 032 prefixes through the end of the season. For season 3, along with the new 20th code system, ABP codes were assigned. The series ended with season 4, but two TVMs followed in January and December 2001, given AER codes (see below) rather than, for example, 5ABP and 6ABP, despite having the same apparent production companies. The first one uses a 99 episode number.
*Secret Service Guy apparently never aired but is dated 1997. This is what epguides.com says!
*Dharma & Greg has another midseason switch, with two twists: after AE79 and AE01-18, the onscreen code switches to ABD19 and then 1ABD20-22, and of course AE is not in the 5+letter pattern (see note above). 19 seems to be the result of confusion or miscommunication. (As one of the rare exceptions to single letters gaining an AB, this was probably further complicated by the existence of 5E/ABE!)
*Two Guys, a Girl, and a Pizza Place (Two Guys and a Girl from season 3 onward) uses 5Z for its pilot (5Z79) and 5Z01-5Z09, but switches to the new format midseason, so 1ABZ10-12. It's possible that the second part of the season was not ordered at the same time as the first, but it's only 3 episodes, so possibly that production was just more amenable to a midseason switch than most others. This recoding does not change 5Z episodes that aired after 1ABZ began.

The curious case of David E. Kelley Productions

Several shows carried the 20thCFT logo, or included 20th among their copyright holders, but didn't use the typical code systems, or didn't use them entirely. A notable group of examples, but one for which 20th had the sole copyright, is the late 90s/early 00s output of David E. Kelley Productions (let's say DEK, referring to the company, not necessarily the man). DEK made a lot of shows with 20th, and yet seemed to take to this late 90s code switch oddly petulantly. Earlier shows like Picket Fences, even Chicago Hope, had normal 20th digit-letter codes under the orderly 90s system (compare also Bochco/Doogie below, also with DEK), and long after the dust had settled, The Crazy Ones in 2013 took the normal three-letter code (even Harry's Law debuting in the 10-11 season, under WB, used only WB codes). But over a decade in between featured a strange run of alternate codes, and a sudden midseason use of a hybrid style as if forced on DEK by 20th just like in 1966.

The grid below illustrates it succinctly. Chicago Hope (also in Table 4) is the only normal example, switching midseason from 5M to 4ABM and continuing for a few seasons with the new system. I have a hunch that the numbers prevented a characteristic DEK coding during the upcoming switch, since it couldn't fall back to 4M, and 4 with another letter would be almost as confusing. For some reason, The Practice and Ally McBeal had strange two-letter prefixes (and one inexplicable pilot number) while other 20th shows were 4_ and 5_ (though the unexplained use of AE for Dharma & Greg instead of a 5_ prefix might be related to AM).

Then when the rest of 20th had moved to three-letter codes, at least eight series got onscreen codes of a shorter hybrid style: their prefixes used the season number as a digit, then a single characteristic letter of 90s style, perhaps as a rejection of the new codes, perhaps out of confusion or lack of guidance. (79 pilots were gone, but some shows had 00 pilots instead!) Many of these conflict with older prefixes, of course (I'm looking at you, Boston Legal), even DEK's own recent Chicago Hope, with most seemingly chosen to relate to the show titles.

Meanwhile, or perhaps only retroactively, these shows did apparently have 3-letter codes (some listed officially onscreen later, or on Fox in Flight, others gleaned elsewhere on the web), all period-appropriate, and most using the forbidden letters "Q" and "U", almost as if they were dealt out for mostly-internal use, or assigned years later as some of the only available period codes.

Suddenly, in October 03, possibly in the space of a week, the short DEK codes and long 20th codes began to appear onscreen side by side, in a variety of styles, mostly but not exclusively treating the 20th ones as secondary. I've confirmed as much as I could, 8P03 to hybrid 8P04, 1H05 to hybrid 1H06, and 4B hybrid as early as 4B04. (See below for hybrid formats.) This hybrid approach, combining DEK and 20th codes (most or all using Q/U even once it was in the open!), lasted at least through the double-length finale of Boston Legal in December 08, the monumentally clumsy "Production #5F12/5F13 (5AJQ12/5AJQ13)"!

Additional code numbers and oddities

• In addition to exemplifying the "00" pilot number, Ally McBeal also uses a single code, 5M16, for one double-length episode in its final season, with no sequence gaps a la 60s series. (And episode code 2M13 is nearly obliterated by a misplaced AMPTP logo, on DVD at least!) See also footnote on Ally.
• The Practice's season 6 premiere is a double-length two-parter, which seems to be coded as 6P01-A and 6P01-B (other similar episodes use a separate number for each part). I have not been able to check this out yet; it may be a similar case to 5M16 above.
• Boston Legal skips episode code 1F18 (1AJQ18), from all I can see.

94-96    2M, 3M Chicago Hope

96 -97

97 -98

98 -99

99 -00

00 -01

01 -02

02 -03

03 -04*

04 -05

05 -06

06 -07

20th code

Notes

4M

5M 4ABM

5ABM

6ABM

ABM

79/01+

The Practice

8402 PR

OW

3P

4P

5P

6P

7P

8P 8P/8ABQ

ABQ

01+

Ally McBeal

AM

2M

3M

4M

5M

ABU?

00/01+

Ally

ALY*

???

Snoops

1S

ADB?

00/01+

Boston Public

1B

2B

3B

4B? 4ADU (4B)

ADU

01+

Girls Club

1G

AGA?

01+

The Brotherhood of Poland, New Hampshire

1H 1H-1AHQ

AHQ

01/ 02+?

Boston Legal

1F (1AJQ)

2F (2AJQ)

3F (3AJQ)

AJQ

01+*

The Law Firm

??

???

The Wedding Bells

1V (1AMU)

AMU

01+?

Table 5: David E. Kelley Productions and its special codes for special people.
*See descriptions above for switch boundaries. Dates: Practice 10/12-19, Poland 10/15-22, Public by 10/17 (previous ep 10/3).
*Ally was a short-lived sitcom companion version of Ally McBeal which is hard to find. Episode guides turn out to be correct: they really did air with the unusual-even-for-DEK codes of ALY plus three-digit numbers, though I've only confirmed the first two (ALY114 and ALY105). The episode titles are the same as their basis episodes' (mostly season 1 and a few season 2) and codes seem to correspond as well (e.g., AM14, AM05).
*Boston Legal ran for 5 seasons, all using the same format.

Back to normal codes: a list of modern main sequence series, followed by some newer offshoots.

Three-letter codes for new series are listed below, with the debut season, some unusual summer timings noted as needed. These are in letter sequence, not ordered by premiere date, unless otherwise noted. Unsold pilots are all unaired, as far as I can tell, and listed with the season their shows would have begun. New entries are welcome, especially for recent years. See Table 4/5 for additional codes given to transitional and DEK shows; see Fox in Flight for a few other offscreen codes.

Note that the sequence keeps its own pace and doesn't roll a letter over for a new season, though it is close to one middle letter per year. A code is assigned to a series as soon as it needs one; note the comparatively early codes for American Dad! (premiered Feb. 05, second episode in May) and The Cleveland Show, for example, which have a long lead time because they're animated.

ABK 97-98 That's Life (see letter conflicts above) (01+)
ABR 97-98 Getting Personal (see letter conflicts above) (01+)
ACG 98-99 Strange World (79/01+)
ACH 98-99 Holding the Baby (79/01+)
ACV 98-99 Futurama (01+)
ACW 98-99 Living in Captivity (79/01+; pilot only "1ACW-79")
ACX 98-99 Family Guy (01+; see also 1ARX01)
ADA 99-00 Roswell (79/01+)
ADC 99-00 Harsh Realm (79/01+)
ADD 99-00 Get Real (79/01+)
ADE 00-01 Dark Angel (79/01+)
ADG 99-00 Judging Amy (01+)
ADH 99-00 Angel (01+)
ADK 99-00 Titus (79/01+; all episodes hyphenated as "#ADK-##")
ADL 99-00 Then Came You
ADM 99-00 Stark Raving Mad (79/01+)
ADU 00-01 Boston Public (01+; see David E. Kelley section, e.g., "4ADU04 (4B04)")
AEA 00-01 Kate Brasher (01+)
AEB 00-01 The Lone Gunmen (79/01+)
AEF 00-01 Freakylinks
AEJ 00-01 Yes, Dear (79/01+)
AER 00-01 The Pretender (post-series TVMs only: 1AER99, 2AER01; see also ABP)
AES 01-02 Reba (79/01+)
AEV 01-02 Greg the Bunny (01+)
AEW 01-02 The American Embassy (79/01+)
AEZ 01-02 UC: Undercover
AFB 01-02 The Education of Max Bickford
AFF 01-02 24 (79/01+; see also AZK)
AFP 01-02 Inside Schwartz
AFY 01-02 Bob Patterson (79/01+?)
AGE 02-03 Firefly (79/01+)
AGG 02-03 The Time Tunnel (only 1AGG79, unaired pilot of unsuccessful reboot)
AGH 02-03 A.U.S.A. (01+?; guides list unaired version of pilot as unlikely 0AGH01)
AGK 02-03 Still Standing (79/01+)
AGL 02-03 Charlie Lawrence (guides say 1AGL00 for first episode of 2 aired, but...)
AGR 02-03 Cedric the Entertainer Presents (79/01+)
AGS 02-03 Oliver Beene (79/01+)
AGV 02-03 The Pitts (79/01+)
AHE 03-04 Miss Match
AHJ 03-04 Still Life (never aired)
AHK 03-04 Luis (79/01+)
AHL 03-04 The Lyon's Den (79/01+)
AHM 03-04 Wonderfalls (79/01+)
AHP 03-04 Tru Calling (79/01+)
AHQ 03-04 The Brotherhood of Poland, New Hampshire (01/02+?; see DEK, e.g., "1H06-1AHQ06")
AHS 03-04 Cracking Up (01+)
AHZ 03-04 The Simple Life (01+; as just 101, etc. at first, see note above)
AJA 03-04 The Big House (01+)
AJD 03-04 Arrested Development (79/01+)
AJE 03-04 North Shore
AJF 03-04 Married to the Kellys
AJN 04-05 American Dad! (01+)
AJP 03-04 The Jury (79/01+)
AJQ 04-05 Boston Legal (01+; see David E. Kelley section, all "1F01 (1AJQ01)" etc.)
AJW 04-05 The Inside
AJX 04-05 Point Pleasant (79/01+)
AJY 04-05 Quintuplets (79/01+)
AKC 04-05 Jake in Progress
AKJ 05-06 Prison Break (79/01+; see also AZM for Resurrection/season 5)
AKK 05-06 The Loop
AKL 05-06 Over There (79/01+; summer-fall 05; episode 2 credits incorrectly say 1ALK01)
AKM 04-05 Stacked (78/02+; see note above)
AKP 05-06 Head Cases (01+?)
AKT 05-06 Kitchen Confidential (79/01+)
AKY 05-06 Bones (79/01+)
ALF 05-06 The Unit (79/01+)
ALH 05-06 How I Met Your Mother (79/01+)
ALJ 05-06 My Name Is Earl (79/01+)
ALR 05-06 Pepper Dennis (79/01+)
ALW 05-06 Misconceptions (from tv.com, never aired; Wikipedia gives intended midseason date)
AMA 06-07 The Winner (79/01+)
AMB 06-07 Vanished (79/01+)
AMG 06-07 13 Graves (unsold pilot, 1AMG79)
AMH 06-07 Standoff (79/01+)
AMK 06-07 Shark (79/01+)
AMP 06-07 Drive (01+)
AMU 06-07 The Wedding Bells (01+?; see David E. Kelley section, all "1V01 (1AMU01)" etc.)
AND 07-08 Fugly (unsold pilot, 1AND79)
ANE 07-08 Company Man (unsold pilot; slate actually says 1AEN79 but must be a typo, so ANE?)
ANJ 07-08 Journeyman
ANK 06-07 The 1/2 Hour News Hour
ANL 07-08 Unhitched
ANM 07-08 K-Ville (79/?)
ANR 07-08 Family of the Year (unsold pilot, 1ANR79)
ANX 07-08 Back to You (79/01+)
ANY 08-09 Life on Mars (01+) (unaired pilot missing credits, could be 79)
APK 08-09 Dollhouse (01+) (unaired pilot "Echo" 1APK79)
APL 08-09 The Ex List (79/01+)
APS 09-10 The Cleveland Show (01+)
APT 08-09 Do Not Disturb
APW 08-09 Lie to Me (79/01+)
APX 08-09 Better Off Ted (79/01+)
ARC 09-10 Glee (79/01+)
ARG 09-10 Modern Family (79/01+)
ARK 09-10 Sons of Tucson (79/01+)
ARV 09-10 Neighbors from Hell (01+) (summer 10)
ARX 09-10 "Family Guy" Presents: Seth & Alex's Almost Live Comedy Show (only 1ARX01, special)
ARY 10-11 Raising Hope (79/01+)
ASA 10-11 Bob's Burgers (01+)
ASN 10-11 Taxman (unsold pilot, 1ASN79; may be written Tax Man)
ASP 11-12 Friends with Benefits (79/01+)
AST 11-12 Napoleon Dynamite (01+)
ASW 11-12 Terra Nova (01+)
ATA 10-11 The Chicago Code (79/01+)
ATB 11-12 Locke & Key (unsold pilot "Ghost Key" 1ATB79; on slate as "P1ATB79", P for Pilot?)
ATF 11-12 Don't Trust the B---- in Apartment 23 (79/01+)
ATG 11-12 Touch (79/01+)
ATM 11-12 New Girl (79/01+)
ATP 11-12 Last Man Standing (79/01+)
ATR 11-12 Awake (79/01+)
ATS 11-12 American Horror Story (79/01+)
ATT 11-12 The Finder (01+)
AVE 12-13 Ben and Kate (79/01+)
AVJ 12-13 Entry Level (unsold pilot, 1AVJ79)
AVR 12-13 Gotham (unsold pilot, 1AVR79)
AVS 12-13 The New Normal (79/01+)
AVW 12-13 The Goodwin Games (79/01+)
AVY 12-13 Family Trap (unsold pilot, 1AVY79; a.k.a. Untitled Mandy Moore Project)
AVZ 12-13 1600 Penn (79/01+)
AWL 13-14 Sleepy Hollow (79/01+)
AWM 14-15 Backstrom (79/01+)
AWN 13-14 Crisis (79/01+)
AWS 13-14 Dads (79/01+)
AWT 13-14 Friends with Better Lives (79/01+)
AWX 13-14 Back in the Game (79/01+)
AWZ 13-14 Gang Related (79/01+)
AXB 13-14 The Crazy Ones (79/01+)
AXH 15-16 Bordertown (01+)
AXP 14-15 Empire (01+)
AXT 14-15 Fresh Off the Boat (01+)
AYA 16-17 Son of Zorn (01+)
AYB 14-15 The Last Man on Earth (01+)
AYC 14-15 Cristela (01+)
AYE 15-16 Minority Report (01+)
AYS 15-16 Detour (unsold pilot, 1AYS01; may be written DeTour)
AYT 15-16 Cooper Barrett's Guide to Surviving Life (01+)
AYW 15-16 The X-Files (revival; 01+; considered season 10-11 but not coded AABX/BABX)
AZC 16-17 This Is Us (01+)
AZF 15-16 Wayward Pines (01+; season 2 after move from FX, see oddities above)
AZH 16-17 Making History (01+)
AZK 16-17 24: Legacy (01+; clearer break from 24/AFF than some nearby examples)
AZM 16-17 Prison Break: Resurrection (01+; considered season 5 of PB, see AKJ)
AZT 16-17 The Mick (01+)
LAB 17-18 The Orville (01+)
LAL 17-18 Ghosted (01+)
LAP 17-18 The Resident (01+)
LAY 17-18 9-1-1 (01+)
LAZ 19-20 Duncanville (01+)
LBW 20-21 The Great North (01+)

Fox21 series (presented in alphabetical order)
RAG 12-13 Brickleberry (01+)
SAB 05-05 Free Ride (01+)
VAA 04-05 Kelsey Grammer Presents: The Sketch Show (01+)
VAB 04-05 Beauty and the Geek
VAL 08-09 Game Show in My Head
VAN 06-07 The Real Wedding Crashers
WAB 08-09 Sons of Anarchy (79/01+)
WAD 10-11 Terriers (79/01+)
WAF 10-11 Breakout Kings (79/01+)
WAH 11-12 Homeland (79/01+)
WAK 13-14 Witches of East End (79/01+)
WAL 13-14 Those Who Kill (79/01+)
WAN 14-15 Legends (79/01+)
WAR 14-15 Tyrant (79/01+)
WAT 13-14 Salem (01+)
WAW 14-15 Rush (79/01+)
WAX 15-16 American Crime Story (01+)
WBB 16-17 Feud (01+)

20th in uncertain direction (all 01+; presented in premiere/release order)
BPJ 19-20 Bless the Harts
CJW 19-20 9-1-1: Lone Star
CFG 19-20 Love, Victor
BZH 20-21 Next
DHW 20-21 Big Sky
GCV 21-22 American Horror Stories
DGA 21-22 Turner & Hooch
DWB 21-22 Only Murders in the Building
HLT 21-22 Our Kind of People
DJE 21-22 Dopesick
HME 21-22 How I Met Your Father
HLX 22-23 Koala Man
NHU 23-24 Tracker
STH 24-25 American Sports Story
UYY 24-25 Grotesquerie
VZN 24-25 Nobody Wants This
LGV 24-25 Doctor Odyssey
ZHF 24-25 Shifting Gears
MPM 24-25 Mid-Century Modern

Bento Box and (mostly) Fox Entertainment Studios (all 01+; premiere order)
BBHB 21-22 Housebroken (not FES)
BBMU 23-24 Mulligan (Universal, not FES)
BBDH 23-24 Krapopolis (DH for creator Dan Harmon?)
BBGR 23-24 Grimsburg
BBHH 23-24 Hazbin Hotel (Amazon MGM/A24, not FES)
BBHG 24-25 Universal Basic Guys (HG for working title The Hoagie Bros.?)

Other 20th/Fox-related code systems and retrocoding

Some production companies for shows distributed by 20th or related to Fox used their own coding styles, and several of those series have been brought into the modern unified system. It's worth checking them out. Because I'm not going season by season, but do want to show the ranges of codes, I list series by their full air season spans.

Steven Bochco Productions

I'll make this short. Most of these shows aired with 20thCFT logos, but the copyright was Bochco's, and the coding styles reflected a production house with no need to overcomplicate. Onscreen codes like these, particularly the all-numeric ones, can be seen in other series here and there, but this company has a few wrinkles: the later incorporation of codes into systems like Fox in Flight and the enigmatic, inconsistent use of alternate prefixes.

The numeric codes are straightforward: Bochco series number and season number (later, series letter). They appear onscreen almost exclusively. Those alternate prefixes are variously reported as O or 0 plus a letter, with no discernible pattern to the letters (later, different first character). They appear less often, and based on the official uses and onscreen examples I can find I am calling them all O. One can see why most codes avoid O and 0 entirely apart from episode numbers! (All episode numbers start at 01, and codes are preceded by "Stephen Bochco Productions #" or similar.) The strangest thing is that the O codes seem to be official (LOC), even when they're not onscreen, and they have less structure than the numeric ones! I've seen them onscreen only in a few shows (and in one official listing in Fox in Flight catalog, see below); elsewhere it's just the numbers, and I've confirmed that on many of these series from actual broadcasts, not just DVDs. Still, I admit the possibility that some might have aired differently. But... why? And why does FIF mix styles too? Why did NYPD Blue switch away from O; did series 8+ use up the other combining letters? Is The Practice season 2 (OW, 97-98) related despite not being a Bochco series?

Note: I have expanded the list to include more of this streak, admitting a few non-20th shows, to illustrate the pattern, in particular the rollover from digits to letters. There is a bit of a gap in the early 00s, presumably E and F shows that didn't make it to air. Since 2005's Over There, which has a normal 20th code (see main list), there may be an end to Bochco-specific codes.

Oddities

• Season 1 of NYPD Blue shows examples of both missing and merged episode numbers: there is no 5104, and a normal-length episode is listed as 5105/5106, suggesting some dropped and combined material. The full season as aired is just 22 episodes, ending with 5124. These are slightly renumbered on FIF.
  The double-length season 9 finale is 5922 onscreen, but sometimes reported as 5922 and 5923 or 5922-A and -B, GA22-A and -B, etc.; Fox in Flight lists both parts separately yet repeats the restyled code 9ABY22 for each!

		Numeric prefixes etc.	O_ prefixes etc.	Notes
Doogie Howser, M.D.	89-93	11 12 13 14	??	FIF: TB11 etc.
Cop Rock	90-91	21	OX
Capitol Critters	91-92	31?	OR/ORO*	Also listed as 0173-91__
Civil Wars	91-93	41 42	OJ OL	Unavailable to check out
NYPD Blue	93-05	51 52 53 54 55 56 57 58 59 510 511 512	OK OV OG OH OT OC OE EA GA HA ?? ??	FIF: 1ABY etc.
The Byrds of Paradise	93-94	61?	OP
Murder One	95-97	71 72 (7223-35 end*)	ON OU (OU11-18*)	FIF: TAON (only)
Public Morals	96-97	81? 01? A1?	OI*	OI or 01? Font no help!
Brooklyn South	97-98	C1	??	CBS, not 20th
Total Security	97-98	91	OR*	Air slate OR conflicts!
City of Angels	99-01	B1 B2	??	CBS, not 20th
Philly	01-02	D1	??	Paramount, not 20th
Blind Justice	04-05	G1	??	Paramount, not 20th

Table 6: Steven Bochco Productions codes (through 05, including non-20th series).
*Capitol Critters codes onscreen really push the O/0 confusion, with the first 9 episodes apparently typeset as ORO1 to ORO9 (I have found some as low as 6); it's not the first time a leading 0 in a two-digit episode number was typeset as an O, yet both characters seem to clearly be Os and not 0s. Then comes OR12 (normal), but ORO 11 (with a space) and ORO10, suggesting it took two episodes in production order for someone to realize it wasn't ORO+number! Wikipedia lists them all as ORO.
*The last eight episodes of Murder One aired in pairs on four dates, and on DVD they are presented as four continuous double-length episodes, with onscreen codes 7223 to 7235 (counting by fours), rather than, for example, 7211/7212. (These four codes are actually the sums of their parts: 11+12=23, etc. Was that the idea?) I do not know how they originally aired, perhaps separate back-to-back episodes with single codes 7211, 7212, etc. instead, or even the O codes; I have learned that modern streaming services do seem to split these eight up. Episode lists that use O codes say OU11-OU18; I do not yet know how the streamers present the codes.
*The credits font for Public Morals makes the prefix equally plausible as OI or 01, and I am really inclined to take it as the former. 01 going between 91 and an A1 isn't totally impossible, but it wrecks the order even more. If it is OI, the numeric prefix could be anything listed. Any more official info out there?
*I've seen one broadcast slate for Total Security that uses an OR prefix (while that episode's credits still use 91), but was Capitol Critters forgotten so quickly? What's going on?

Fox Television Studios (etc.)

For over a decade (a sign of quality), and starting at about the same time as 20thCFT's revamped three-letter system, a very good system was in use at Fox Television Studios, though I am fairly partial to post-60s 20th styles because the letters really help avoid ambiguity. Codes combined three sections separated by hyphens: a sequential series number (or pilot sequence), a two-digit date (start of production year), and a three-digit season/episode number (179 for pilot, 101, etc.). Even the best 20th codes miss one of those details, and FTS codes even highlight how some pilots are made the previous year. Consistency was a little low, with some series skipping a separate pilot sequence designation, others using that for the full first season. The series number seems nice and orderly, even when "50"s started appearing at the start of all of them, but it's possible there are two concurrent sequences going, especially since 5012 not only conflicts with 12 but predates it by several years. (Alignment of B and A/C codes as seen below supports the existence of 2 or more sequences/subcompanies. Not all of these shows identify Fox Television Studios by logo or copyright, though Wikipedia seems to lump them under it.)

Suddenly, in 2011, these long but descriptive code triads were abandoned in favor of a more compact system for onscreen use, one very close to 20th's own except for one detail. Each series got a three-letter code (some or all of which had been assigned years before, judging from Fox in Flight catalogs of 2008), and used it plus the season and episode number from then on, except that the series code came first. Why was it BCI501 and not 5BCI01? (Why is the letter I allowed, along with U and perhaps more?) Did this sequence and others prevent a 20thCFT rollover from A to B?

As early as 2007, some (although not all) series supplemented the official production code with what I think is meant to be an air order season-episode number preceded by an "S". (79s, or 179s, often didn't have those, but counting with episode number 01 began after the pilot.) This could also be a mouthful, especially in double-length episodes, such as Burn Notice's season 1 finale (episodes 11 and 12, or one long 11), which is declared "Production: # 5037-07-110/111/S110/S111". Several series, noted in the footnote below, use S codes that are not in air order, so perhaps they do mean something else. And in almost every case they got abandoned by the mid 2010s anyway.

The grid below includes three-letter codes for series that did not use them onscreen, pulled from the Fox in Flight catalog. Again, these may have been assigned when the shows were new, or well before 2008. It also lists some examples of the S codes and points at which they changed. Lights Out aired right on the cusp of the format change, after some later-in-sequence series' full seasons, but I've been unable to examine it to see what system it uses; it could go either way. Note that slashes in 179/101 are for brevity and not examples of on-screen combinations.

In 2014, Fox Television Studios merged with Fox21 (see W__ codes above) into Fox 21 Television Studios, though the shows I've looked at did not all switch logos immediately, and all kept their code styles. More recent history is a topic of future examination.

		Up to 10-11	11-12 and later/ Alt code	Notes and S-style examples
The Hughleys	98-02	2-98-179/101+ 2-99-201+ 2-00-301+ 2-01-401+	AAB
Oh Grow Up	99-00	10011-99-179 04-99-101+
Malcolm in the Middle	99-06	10012-99-179 06-99-101+ ... 06-05-701+	CAB
Murder in Small Town X	00-01	5008-00-101+		Or 5006?; no 179?
The Bernie Mac Show	01-06	10041-01-179 08-01-101+ ... 08-05-501+	CAS
The Shield	01-08	5012-01-179/101+ 5012-02-201+ ... 5012-05-501+ 5012-05-512+* 5012-07-701+
John Doe	02-03	10-02-179/101+
Method & Red	04-05	11-04-178/101+		"178" typo for 179?
Listen Up	04-05	10068-04-179 12-04-101+
Living with Fran	04-06	13-04-179/101+ 12-05-201+*	CBR	S2 "12" typo?*
Thief	05-06	5023-051-179/101+		"051" meant to be "05"?
Help Me Help You	06-07	10097-06-179 16-06-101+
The Riches	06-08	10095-06-179/101+ 5034-07-201+	BCF
Mr. & Mrs. Smith	07-08	1018-07-179		Unsold pilot; "18" meant?
Burn Notice	07-14	10105-06-179 5037-07-101+ ... 5037-10-401+	BCI501+ BCI601+ BCI701+	No extra pilot code 5037-07-102/S101 BCI501/S501
White Collar	09-15	5039-08-179 5039-09-101+ 5039-10-201+	BCW301+ BCW401+ BCW501+ BCW601+	No extra pilot code 5039-09-103/S103* BCW301/S301* BCW601
The Good Guys	10-11	5042-10-101+	BDE	5042-10-113 /S113; no 179?
The Glades	10-14	5046-09-179 5046-10-101+	BDF201+ BDF301+ BDF401+	No extra pilot code 5046-09-101/S101* BDF201/S201
Lights Out	10-11	???/only BDA?	BDA, 179/101+	Debuted after BDE/BDF S1
The Killing	10-14		BDH179/101+ BDH201+ BDH301+ BDH401+	BDH179/S179 BDH101/S101 BDH401
The Americans	12-18		BDU179/101+ BDU201+ ... BDU601+	BDU179/S179 BDU101/S101 As Fox21 TS for S3+
Graceland	13-16		BDV179/101+ BDV201+ BDV301+	BDV179/S179 BDV101/S101 (+205-213) BDV201/s201 (to 204) BDV301; S3 as Fox21 TS
Sirens	13-15		BDZ179/101+ BDZ201+	No extra pilot code BDZ101/S101*
The Comedians	14-15		BEF179/101+	No S codes; as Fox21 TS

Table 7: Fox Television Studios codes and cutover in brief.
*Season 6 of The Shield is numbered as the second half of season 5 because it was conceived as one long season, but FX held that half back. In a sense, the seventh aired season should use codes for a sixth production season, but that's not what happened. All of season 6 aired in 2007, after over a year's hiatus; the final season waited even longer and arguably could be filed as 08-09, although its codes do reflect a production year of 07-08.
*Season 2 of Living with Fran clearly shows its series code as 12, but it should be 13 (and 12 conflicts with Listen Up, or would, if that had gotten a second season). How'd that happen?
*The S-style codes for White Collar (except season 4, which is fully in order) and season 1 of The Glades do not follow the air or production order; apart from being off by one for a pilot, other shows' codes are in air order. Do they mean something else, did producers expect another air order, or what? (Bonus oddity: White Collar's deleted scenes on just the season 5 DVDs are identified by the dual code minus BCW and divided by an underscore, e.g., "501_S503"; they are presented in production order too.) And Sirens (season 1, I haven't inspected 2) uses S codes weirdly and redundantly matching the production codes.

Fox in Flight, iTunes, etc.: rewriting history

With a broad catalog of series across the Fox brands, including decades-old ones and series acquired from other companies, all with a mismatched and often conflicting set of production codes, the company had some work to do to offer series for licensing and direct consumer purchase through online marketplaces. All of the research I've done has been based on the "Fox in Flight" page, an online catalog (c. 2007-16) that I think was meant to let airlines select what they would offer as in-flight entertainment (perhaps as linear programming or on-demand by episode name only, the production codes likely for internal use); I am told the codes below are or were used on places like AOL Video and iTunes, too, but have not investigated much further or sought out more recent examples. The idea is to show a curious slightly-inside look at the industry and how it adapted the codes, and I thank Brian for this pointer.

The Fox in Flight choices, last seen in 2016, are available here. Many offerings are a curious subset of seasons or episodes, with random omissions and sometimes just a few episodes available at all. A number of double-length two-parters are offered as separate episodes (with their own single codes), but perhaps they could only be licensed and viewed as pairs. And some of the adapted episode code lists take major liberties with the two-digit episode numbers (I can't list them all). This is also where some margin-dwelling 20th shows' codes are revealed, with a few twists, and a good deal of fairly intuitive 90s code backnumbering. Most notable for this document: 3G episodes of The Simpsons, rather than being adapted into the 7ABF range, make rare use of the letter "I", becoming 7ABI01-04.

Based on the selection on FIF, I have made these categorizations.

• Shows using the existing 3-letter codes for all of their episodes are listed that way. This includes all normal A__ codes and Fox21 WA_ codes, plus the internal A__ codes for pertinent Kelley shows that double-coded (Boston Public, Boston Legal). These total in the dozens.

• Shows that straddled the boundary from the 90s or outside styles to the new system back-number the older episodes accordingly (Simpsons 7G = 1ABF, 7F = 2ABF, etc.; 3Gs become 7ABIs under this style and 31-33s are not renumbered). This includes relevant double-coded Kelley shows (Chicago Hope, The Practice now with pilot 1ABQ79) and The Pretender (severely renumbered, into air order?).

• Two peripheral shows gain 3-letter codes I've only ever seen officially on FIF, though perhaps they were used internally during production. NYPD Blue (see Bochco notes), which straddled the code system change, is listed with appropriate transitional code ABY and some renumbering. Martial Law (semi-20th with no onscreen codes, began 98-99) has ACU codes in air order (and its use of U is similar to that of Kelley shows).

• Older shows with 4-character alphanumeric codes that didn't stretch into the new system tack "TA" or "TB" onto the front, though some shows use codes from alternative systems, including non-onscreen variants. Hyphens and part numbers are omitted. For some reason, Daniel Boone seasons 1 to 3 are the bare 4-digit codes in these listings, but may be intended as TA+code; season 5 has TA and seasons 4 and 6 just aren't listed. The TA/TB system seems designed to avoid overlaps (note all TAs are of different letter-number patterns except the fairly well behaved all-number ones, both TBs...), although actually none of the offerings of these six shows do overlap (Daniel Boone and Doogie Howser's season 4s would, but aren't in the catalog!). Note that the TA prefixes did not prevent The Simpsons from using TABF codes.
  
  TA:
  The Green Hornet (TA9801 etc., renumbers/flattens 2-parter codes)
  The Paper Chase (TAT701 etc.; original season only, no pilot)
  L.A. Law (TA4L01 etc.)
  Murder One (TAON01 etc., not TA7101 onscreen style; no season 2)
  Daniel Boone (no TA on first 3 seasons, 7426 2-parter one entry; season 5 TA3001 etc.)

  TB:
  M*A*S*H (TBJ305 etc., double length episodes listed separately; no pilot)
  Doogie Howser, M.D. (TB1113 etc.)

• Shows from other recent Fox spinoff brands like FTS and FX use a three-letter prefix and then 3-digit season-episode code, perhaps deviating from the usual component order to match the FTS one. FTS prefixes are orderly despite not appearing onscreen until 2011, with lots of them listed on FIF as early as 2008 as well, suggesting they had these codes somewhere official for years. The first letters A-D might classify the shows by co-production companies (though the fact that A-C-B fit precise bands chronologically for all series identified so far is also striking). For FTS shows before 2011, the codes are backnumbered, including using 179s for pilots.

  AAB### 98-02 The Hughleys (see also AA_ identifiers above)
  
  BCF### 06-08 The Riches
  BCI### 07-14 Burn Notice
  BCW### 09-15 White Collar
  BDA### 10-11 Lights Out
  BDE### 10-11 The Good Guys (no 79)
  BDF### 10-14 The Glades
  BDH### 10-14 The Killing
  BDU### 12-18 The Americans (Fox21 TS for season 3 up)
  BDV### 13-16 Graceland (Fox21 TS for season 3)
  BDZ### 13-15 Sirens
  BEF### 14-15 The Comedians (Fox21 TS)
  
  CAB### 99-06 Malcolm in the Middle
  CAS### 01-06 The Bernie Mac Show
  CBR### 04-06 Living with Fran
  CBW### 05-06 Killer Instinct
  
  DDZ### 08-12 Kendra (no onscreen codes; no 79; 50 and 51 codes not seen elsewhere)
  

  FX/FXP shows (using a lengthy but fairly straightforward onscreen style) drop their native codes and get YB_ and YJ_ codes instead (sequential vs. hand-picked FX digraphs?); the strangest thing by far is that for It's Always Sunny in Philadelphia, besides severely renumbering some episodes, it eschews the alphabetical season codes past season 9 in favor of a new prefix! The list below includes the FX "X" prefixes for comparison (prior to 2010 there was no X; "x" stands for transitional series). These shows all start at 101. (See also Wayward Pines above; it was not on FIF but its YJU code should be noted here. Also not on FIF is Outcast, debuting summer 16 with YSU101, but that's Fox International Studios; whether this is a successor to YJ_ or a parallel sequence, and other related topics, may be examined later.)
  
  YBP### 05-14 xIP It's Always Sunny in Philadelphia (season 1-9) (Xmas = 597)
  YBY### 14-   XIP It's Always Sunny in Philadelphia (season 10 YBY101+, 11 YBY201+, +?)
  
  YJE### 09-16 xLE The League
  YJF### 10-15 XCK Louie
  YJH### 11-14 XWL Wilfred (all firmly summer airdates)
  YJX### 14-19 XYW You're the Worst
  YJZ### 14-   XFO Fargo

• Old shows from MTM Enterprises/Productions (which 20thCFT acquired) use a similar 3-letter format to 20th shows, but with YA_ codes instead (not entirely chronological). These shows tended to have 4-digit codes a little like 20th's 60s style, complete with separate pilot codes, but repeated their first 2 digits quite a lot (see examination below). They also skipped over episode numbers very often, and the original designations are generally reflected here except for the pilots. (Actually, the older MTM shows often had extra prefix digits, pilots even more, but those aren't important here. Further examination below.)
  
  YAD 78-82 WKRP in Cincinnati (S1, pilot 1YAD68, may be renumbered, no onscreen codes)
  YAL 80-87 Hill Street Blues (pilot 1YAL25, 2-parters ...13A/13B/14A/14B now 1YAL13-16)
  YAM 82-87 Remington Steele (pilot 1YAM79)
  YAN 70-77 The Mary Tyler Moore Show (no separate pilot code)
  YAU 82-90 Newhart (pilot 1YAU79)

• Brian reported DYO for Dynasty (1DYO01, etc.), another rare use of "O", but listings are not on FIF archives.

FIF is not the only place where alternative code formats could be seen, but I haven't seen many lately, primarily air season/episode combinations (#-##, #x##, S#E##) that have nothing to do with production codes. When I began this guide, some online TV guides used the 4-character Simpsons codes when available but then (also 4-character) adaptations for the "ABF" years. AABF01 became 1001, and so on, matching their simpler production code listings of other series.
Other people may use production codes in hotel-room format casually when the series itself is known, for example, in discussing Futurama, "410" for 4ACV10. This doesn't work too well for 90s Simpsons without backnumbering or past season 34 but I will make shorthand notes for Simpsons F23 or American Dad! G09, etc.

Non-20thCFT styles for comparison and interest

Other production companies, of course, have different methods. Many are purely numeric and consist of the same room-numbering sort of system: 101 is season 1, episode 1, etc., and these don't tend to appear onscreen. Others have special prefixes that do appear in the credits. Two expansive systems are explored here. If you spy a code in another company's show, dive down that rabbit hole!

MTM Enterprises

MTM Enterprises, MTM Productions, etc. (named after Mary Tyler Moore), also closely linked with the name Company Four and in later years seen with names like TVS and Family Entertainment, is a medium-sized example worth examining for a few reasons. It's very orderly on the whole, through a few slight variations in style, although with a few perplexing elements and one drawback that impacts uniqueness. It was only in operation for about three decades, and neither time nor scope of production stretched the scheme too far. With scattered exceptions, its codes were displayed in credits for its whole existence. Most of its productions can be found and no new ones are adding uncertainty. And it's linked to 20thCFT directly through one show and indirectly through the Fox catalog, since it was eventually acquired by Fox.

Because some of the code system eras are very short and others make for cumbersome layouts, the tables below are arranged to fit the space, but they are easy to follow. Bold and italics indicate the same as above. Since early years split codes into blocks of 50, lowest-numbered full codes are listed there; two-digit (and later three-digit) prefixes for episode codes are used after about 78. A handful of shows seem to have no codes onscreen or in online guides, and as with 20th the pattern is unclear, but entries are omitted only if I can't find anything to report. Also, reunion specials etc. in the 90s just don't seem to have codes in the examples I've found, so as a rule I'm not listing them.

This fact does not affect the listings in any major way, but MTM codes have two notable aspects compared to the other companies' in this document. One is that production and air order seem to differ the most, with many MTM seasons just looking very jumbled (but unless the stories connect, isn't it somewhat arbitrary to air things in the order scripts were assigned?). The more interesting is that episode codes are often missing or skipped over, perhaps from abandoned plotlines, etc., instead of shifting or reassigning numbers to fill the gaps. While other companies occasionally have some gaps like this, it's an unusual season of an MTM show that doesn't. (Only early Lorimar years come close.) In fact, several seasons here do not have an 01, 02, etc., and many shift a fairly high-numbered episode to the start that seems to suggest the point a rewrite began. But apart from some evidence of this in the tables, I'm not getting into detail; take a look at lists if you like! In addition, it's worth pointing out that many two-parters, whether aired together or not, use the same code (often with an A or B suffix) rather than two separate ones.

70-77: the early years

MTM was formed to produce The Mary Tyler Moore Show and it had a very straightforward code scheme: two-digit starting year of the production season (compare, e.g., FTS), two-digit episode code. Two years later, The Bob Newhart Show came along, and since seasons did not exceed 50 episodes, it took the top half of the range, with episode codes starting at 51. This worked for two combined seasons, and the four total make up the first era of MTM codes. (Pilot codes are coming up.)

For the 74-75 season, though, MTM was going to be producing several more shows, and the system had to expand. Now only the last digit of the year would be used, followed by a digit and half-century of episode codes that persisted per show. For example, MTM took 4001 and up, 5001 and up, etc., Bob Newhart 4051, and so on. As shows came and went, their characteristic digit/half could be repurposed. The 50-episode split continued for much of the 70s, and this overall scheme lasted for about 17 years (the mathematically inclined may notice a problem here).

Pilots and TVMs (and those in between), however, are mostly a mystery. They usually get special codes, as seen in other systems here, but these are something else. While most codes are four digits, these often have one or two extra quartets separated by hyphens. If there are three groups, the first is always 0311, suggesting a larger, perhaps industry-wide scheme, maybe with 0311 representing MTM. The middle one, or first if there are two, could be a specific company, studio, person; note in this table and the next that some middle codes do appear more than once. And the last, sometimes seen just on its own (e.g. 9780 below could be short for 9000-9780, itself short for 0311-9000-9780, but the guide only lists 9780, and many onscreen codes omit parts anyway), seems to be a sequential code as usual, at least when considered on a per-middle-quartet basis. But by and large they seem very random and incomprehensible. See also the original Waltons TVM and its own similar code under CBS; there may be a lot under the surface here.

Oddities

• Episode 21 in season 1 of The Bob Newhart Show seems to be missing its code (7273).
• Rhoda uses a single code (4160) for a double-length episode; this is typical for MTM but the examples are short enough to list so I will.
• Several episodes of Phyllis seem to say 6216, despite their credits listing different people; I'm not listing duplicated codes in general but the sources seem reliable here so it's especially puzzling.

The Mary Tyler Moore Show	70 -71	71 -72	72 -73	73 -74		74-75	75-76	76-77
	7001	7101	7201	7301		4001	5001	6001
The Bob Newhart Show			0311-5536-7296* 5536 7251	7351		4051	5051	6051	+
Rhoda						4151	5151	6151	+
The Texas Wheelers						0311-9000-9720 425x
Paul Sand in Friends and Lovers						4494?* 4201
The Bob Crane Show						4???*
Doc							???? 5101	6101
Phyllis							6524 5201	6201
Three for the Road							0311-????-6521 5251
Just an Old Sweet Song (TVM/pilot)								9000-9797
The Tony Randall Show								9780 6351	+
Something for Joey (TVM)								1523-0303

Table 8: MTM codes 72-77.
*The Bob Newhart Show: The long code is for the unaired pilot (included as a DVD extra), and the short version is on the revised pilot that aired as an episode (9th, actually). It's surprising that the middle set of digits is used.
*The unaired Paul Sand pilot is listed online in a way that suggests 4494 is right, but I could be wrong, and of course I haven't seen it.
*A few episodes of The Bob Crane Show are available but the codes are very hard to read. Squint one way and they could be in a 4101 sequence; squint another way and they might start with 43 or something else.

77-82: simplification

The previous system is still in place, except that 77-78 seems to be the last year new shows have to share the second digit (Rhoda would continue starting at x151 through its run, ending in 78-79). From then on (or by 79-80 anyhow), until the 90s, each second digit in episode codes would stand precisely for one show for its run; the maxinum number of concurrent productions drops from 20 to 10 but MTM never had even that many irons in the fire, so this works well.

But now occasionally another set of digits would appear on episode codes. These seem to represent a show, since they never change, but could also mean a studio or company or something; I just don't have any more examples than The White Shadow and Hill Street Blues, and those codes don't appear in anything else I've seen. It's worth noting that both of these are listed under Company Four (many but not all of these longer codes are!), and actually HSB's copyright goes back to MTM at the same time the 8005 is dropped, but White Shadow is always Company Four, so I'm still stumped.

Pilots and TVMs continue as before, though MTM seems to stop making the latter around this time (some 90s TVMs it's associated with belong to other companies and don't have onscreen codes).

Oddities

• Both Rhoda and The Tony Randall Show seem to skip episode numbers 51 and 52 in the 77-78 season; this is not unusual for MTM but that's why the ranges start at 53 below.
• The Betty White Show does not seem to have onscreen codes after its pilot, but unlike most other omitted codes these are reported online at least. It's the middle set of digits in the pilot code I am having the most trouble making out, by the way, but if 0768 can be believed for We've Got Each Other, maybe it's not a 6 here!
• Likewise, season 1 of WKRP in Cincinnati does not have any onscreen codes, for reasons I can't guess, and the 80 below just seems reasonable. Episode guides list codes that do not seem to match up with anything onscreen later or air/production order, and so I see no reason to believe they match season 1 codes in any way, but Fox in Flight codes may be based on the unseen ones, and since FIF has a high pilot code that suggests a separate one here too.
  WKRP has a handful of two-parter (and combined) codes in various styles for seasons 2-4: "9008-A" and "9008 B" (or maybe a tiny hyphen but it's hard to make out) for a two-parter on separate weeks and "9027" alone on a double-length episode; "0010/0016" (combined scripts?) on a single half hour episode and "0022-A/B" on a double-length one; "1004-A" and "1004-B" for one more two-parter on separate weeks.
• Season 1 of Hill Street Blues ends with two two-parters that seem to be presented as four separate episodes despite each pair sharing an airdate (this is what is on DVD, but I can't rule out that they aired as combined episodes originally), and their long onscreen codes end in "0413A", "0413B", "0414 A", and "0414 B" (very thin space on B). See also renumbering for FIF.

		77-78	78-79	79-80	80-81	81-82
The Bob Newhart Show	^	7051
Rhoda	^	7153	8151
The Tony Randall Show	^	7353
The Betty White Show		0311-0303-0768? 7601
Lou Grant		7501	85	95	05	15
We've Got Each Other		0768? 7551
WKRP in Cincinnati			???? 80?	90	00	10
First You Cry (TVM)			0311-3211-0437
The White Shadow			5216-4501 3264-8101	3264-91 91*	01
The Last Resort				92
Paris				???? 93
Vampire (TVM/pilot)				9200-2027?*
The Boy Who Drank Too Much (TVM)				3211-0597?*
Carlton Your Doorman (pilot/special)				5465-4006?*
Fighting Back: The Story of Rocky Bleier (TVM)					9200-2033?
Hill Street Blues					0311-9300-3021 8005-04	8005-14	+
Thornwell (TVM)					3211-0690

Table 9: MTM codes 77-82.
*The White Shadow codes drop the 3264 early in season 2, though not in air or production order. It looks like episode 7 (9133) and then 9 (9105) onward with just the four-digit codes.
*Though there are many hard-to-read codes in these tables, these three jump out as especially tantalizing. All copies of Vampire I can find are very dark but this code seems about right; The Boy Who Drank Too Much could easily end in 0097 or something but its place in the 3211 sequence suggests the 5 at least. Carlton Your Doorman (a failed animated spinoff of Rhoda, available on that show's final season DVDs) has a perfectly crisp transfer but almost no contrast between the text and background so it's maddeningly tough. 4006 could be 4000, or 1000, or 1006...

82 onward: a few final changes

The 80s continued with the simplified system. Pilots seem to have been simplified to 4 digits and from Newhart to the early 90s they seem to come from the same single sequence (at a rate of about 30 per year!). But now the first digit starts to create conflicts with codes from 10 years before, and this seems to bother no one. It may be an admirable goal to create unique codes company-wide, but unique within 9 years in either direction (not counting pilots, which have no special pattern to avoid this) is pretty good too, and none of these shows got close to an eleventh season. Still, these prefixes managed to continue, occasionally overlapping with old ones, until about 90-91.

Production (of scripted TV) dwindles in the 90s and examples are less frequent so it's harder to paint a confident picture, but the three mid-90s shows here suggest a cutover in 91-92 to a new system: rather than calendar year, the first digit seems to stand for season number, with the second digit still standing for the show (compare the late 90s 20thCFT change). It works either way for The New WKRP, but the updated version is the simplest way to explain Evening Shade and Christy.

There's a gap year where MTM didn't seem to make anything (the only entry that year on Wikipedia is for Family Challenge, a game show with no codes and a branding of—really—Company Six). After that, there is a final burst of production with one more system. Ironically (in the light of MTM's imminent fate) it seems to allow for more than ten concurrent projects (or dozens of non-recycled show codes for many years), using a leading zero ahead of or as part of a show-specific number, then a season digit and two-digit episode code. (Some of these separate the last two parts with a hyphen.) It does not appear that a separate pilot sequence exists anymore (compare 20th's move away from this in the 80s and WB's continued use).

It's also notable that many 90s shows under MTM include their episode titles on the copyright page, near the production codes, which is extremely handy and considerate. I've seen this on The New WKRP in Cincinnati, Sparks, The Cape, Bailey Kipper's P.O.V. (when codes are there, see footnote), and Good News.

But at the end of the 90s, the slow and complicated web of mergers and renaming concluded, leaving MTM basically out of business; The Pretender continued on as a 20thCFT property (though still retaining MTM copyright for most of its run) and those codes are detailed above. Good News and Sparks seem to have a mix of MTM and 20th branding and copyright in the 97-98 season from episode to episode, too, but I have not been able to examine all episodes.

Additional code numbers and oddities

• Remington Steele's double-length season 2 premiere is coded as only 3709 (but with an unusual typeface and off-center placement, and no 3701, which is not entirely odd for MTM); a similar double start to season 6 is "6702/6708" (and although again skipped numbers are not unusual here, 02 is the only episode number outside of the 06-10 range for this very short season).
• "Pilot", the first-aired episode of St. Elsewhere, actually has a code of 2313, suggesting perhaps a major retooling of an unaired pilot partway through production; unusually for MTM, season 1's 22 episodes do not skip a code at all!
• Beverly Hills Buntz (a spinoff/continuation of Hill Street Blues, even claiming its show digit) does not have onscreen codes in any episodes I could find (which is most of them).
• The double-length premiere of Capital News has just the code 9406, and is called "Pilot" despite having a regular episode code. The actual pilot with code 1423 is a later-aired episode, according to the copy I found.
• The double-length premiere of Evening Shade has one code, 0601; a two-parter in season 3 has just the code 3628, although I can't tell whether it aired as a combined double-length episode originally, and on DVD it's in two parts, each with the same code and no A/B designation.
• The New WKRP in Cincinnati adopts the codes 1890 and 2890 for its double-length season premieres, or rather special pre-season clip shows, and both seasons do include 01 codes.
• Christy's double-length premiere has no onscreen code; possible reasons vary. The season 2 premiere (or teaser, as the rest of the season began months later) is double-length with the code "2011/12", although there is no 2001, again suggesting an abandoned initial direction. (Later TVMs are from another company, neither MTM nor 20th.)
• The Cape has a double-length opener coded 01100, but no 01 or 02.
• The Pretender has only one skipped episode number (03105 in season 1); I previously listed this under 20th oddities so I'm keeping it even though it's not remarkable under MTM. All four seasons have double-length finales, each with two codes.
• Some episodes of Good News seem to omit the hyphen toward the end of the season, though I've only been able to examine a few low-resolution examples.

		82 -83	83 -84	84 -85	85 -86	86 -87	87 -88	88 -89	89 -90	90 -91	91 -92	92 -93	93 -94	94 -95	95 -96	96 -97	97 -98
Hill Street Blues	^	24	34	44	54	64
Remington Steele		0903 27	37	47	57	67
Newhart		1210 21	31	41	51	61	71	81	91
St. Elsewhere		23	33	43	53	63	73
Bay City Blues			38
The Duck Factory			36
Mary					56
Fresno						1325*
The Popcorn Kid						1334 65
Beverly Hills Buntz							74
Eisenhower and Lutz							77
Annie McGuire								86
FM									1426 96?*
City									1413 90
Capital News									1423 94
Evening Shade										06	26	36	46
You Take the Kids										1458 07
The New WKRP in Cincinnati											18	28
Christy													???? 10	20
Sparks																071-	072-
The Cape																011
The Pretender																031	032	*
Bailey Kipper's P.O.V.																021? 021*
Good News																	091- 091

Table 10: MTM codes 82+.
*Fresno is a miniseries and in the credits I've seen all parts seem to use the same code, suggesting a single pilot/TVM/special code was used for the whole thing, but I could be missing something.
*This is what most FM codes look like, but at least one seems closer to a 95, and the seeds of doubt are sown. MTM reassigns the second digit to other shows quickly after cancellation, so being sandwiched between two other 6s does not rule out a 6 here.
*The Pretender: See 20thCFT for ABP and AER codes for season 3 and 4 and TVMs.
*Early episodes I can find of Bailey Kipper's P.O.V. do not have codes (or titles) in the credits, but later ones do. However, these copies seem to be split between American and British airings, so could the credits have been redone for export?

Warner Brothers TV, Lorimar, etc.

There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
There is another theory which states that this has already happened.

—Douglas Adams, The Restaurant at the End of the Universe

WB before 93: nothing to see here

The earliest codes I've found start in the 70s. As noted, none of these are onscreen, but they certainly seem to be consistent. Few pilot codes are known, although the ones that are listed fit a pattern. This whole period uses variable-size code blocks only about as large as necessary, with some creative dips into unused segments for supplementary purposes, and some very small orders at times (see footnotes). But every single reported code does follow the third-digit rule!

Even though Lorimar merged into WB in early 89, changing code styles immediately and putting the codes onscreen soon after (see below), codes for WB-branded shows continued in the old pattern until the end of this period, even venturing into the 187 prefix a few years after Lorimar had used it (just before merger), with at least one collision in codes.

• 206: Pilots (as early as 206717 in 83, as late as 206813 in 93). It seems reasonable that others would have them, but I mustn't assume.
• 166-167: Episodes from 72 (or earlier) to 83. In this small sample of shows, 1663xx and 1664xx codes seem to be skipped, only to be claimed in 79-80. Reluctance to jump to 167 too early?
• 185-187: Episodes from 83 to 93.
• Why 175-177 were skipped stumps me, but see 2002! Note also that Lorimar codes would go through this range in the late 80s, following a pattern than had been established in 82, but this is well before the merger.

	71-72	72-73	73-74	74-75	75-76	76-77	77-78	78-79	79-80	80-81	81-82	82-83
Kung Fu	??????	166141	166201	166251
Wonder Woman (The New Adventures of Wonder Woman)					?????? 166531	166601	166701	166831
Alice						?????? 166551	166661	166801	166931	167201	167461	167621	+
The Dukes of Hazzard								?????? 166861  to 65 166871  to 78	166961 166401* 166431*	167121	167401	167701	+
Flo									166361	167231  to 44 167351  to 59

		83-84	84-85	85-86	86-87	87-88	88-89	89-90	90-91	91-92	92-93
Alice	^	185201	185571
Dukes/Hazzard	^	185101	185501									+
Scarecrow and Mrs. King		206717 185301	185431	185741	185901
Night Court		206719 185361	185601	185711	185931	186201	186461	186631*	186931	187231
Growing Pains				206740 185801	185961	186101 186291/2* 186365*	186431	186701 186695/6*	187011	187201		*
My Sister Sam					206754 185881  to 92 186091  to 99	186131
Just the Ten of Us						186293*	186531	186731
China Beach						?????? 186371	186501	186801	187041
Murphy Brown							206772 186561	186601 186690-2*	186851	187161	187401	+
Kung Fu: The Legend Continues											??????	+

Table 11A/B: WB before onscreen codes (to 93). Dashes and slashes denote multiple episodes.
*The first two seasons of The Dukes of Hazzard seem to be made up of very small orders spaced fairly close together. Besides the 5+8 episodes of season 1, season 2 starts with most of 166961-166973 from the normal sequence (two aired fairly late including one holdover), then we see two dips into the older numbers, 166401-166409 and then 166431/32/33A/33B to bridge season 2 and 3. Some later episodes have a variety of A/B codes but are not worth enumerating here!
*Season 7 of Night Court is often listed with 186331+ codes, but I see some 6s and they fit much better. There are so many typos and other little mistakes that I can be skeptical.
*The first two odd Growing Pains codes are a backdoor pilot for Just the Ten of Us (which also explains its odd starting number). 186365 is a clip show; the final two seem to be normal episodes at the end of the season, but with separate spare numbers for some reason. None of the main blocks of codes seem to be at their limits (see Murphy Brown). There are also two TVMs from the 2000s, which I will note here because they're too odd to fit anywhere else. 2000's The Movie is a WB production but lists no code (some just don't, even then, and I usually don't feel the need to list them); 2004's Return of the Seavers is still WB but lists "Production #0122500111", which is unlike anything else I've seen. Weird!
*The last three episodes of Murphy Brown season 2 pull from the same decade of spare codes as that spring's Growing Pains extras, and again with no apparent need. If both shows had sudden orders for a few more episodes, perhaps some policy forbade using available consecutive codes from the original blocks. Who knows?

Lorimar before 93: a system is born

As with WB, the early years do not use codes onscreen but what is reported seems consistent. A few systems (both seeming to precede the third-digit rule) are in use, with blocks of both unusual size and unusual alignment, and many skipped episode codes. These are detailed below. It is remarkable how similar the WB and Lorimar styles are on the surface despite coming from different companies. In January 89, WB and Lorimar merged, and almost immediately codes jumped into a new format (everything beginning with 4) at equivalent points in the new blocks, which began appearing onscreen in the fall with a few stragglers. Extra detail is given on the 88-89 recodes and 89-90 onscreen debuts in the table, with all but two of the latter confirmed precisely.

These are the first onscreen codes for either company, later than any other major system explored here; for continuity of code system evolution, the onscreen codes notably rival those of 20thCFT, especially if 20th is limited to the more structured codes with origins in the early 90s!

Many early codes appear very close to the IATSE logo, some arranged as if to suggest the number is connected to that (even reading "IATSE #" in one line); it is probably just layout convenience. As years go by and the word "Production" appears more often, this impression is lessened.

• YYMMDD/?: Pilots that I am aware of (in 77 and 79), or at least the numbers I've seen seem to indicate some production date. Valerie is a mystery. Whether these are official codes I can't say; separate pilot codes seem very rare here.
• 188-189: Episodes from 76 (or earlier) to 82. As with WB, in 79-80 some codes seem to dip into the 1881xx range, though I'd be willing to believe the examples I've seen were really 1887xx or something. None of it's onscreen, anyway!
• 171-177, 187: Episodes from 82 to 89 before the WB merger. Here there is some structure, with the third digit reflecting the production season, all sequences starting at 01, and the fourth digit tied to the show, mostly. The addition of 187 alongside 177 in 88-89 may be an attempt to maintain the structure, especially if the fourth digit was exhausted by shows not seen here. These first few prefixes are the main exceptions to the third-digit rule.
• 475 (0xx): Pilots after the merger; the earliest I have are in the 030s in 90, but I imagine they began around 001 as soon as the new numbering scheme took effect. This pilot sequence continues for almost two decades and is one of the most stable parts of this system. See footnote on Family Matters and its backdoor pilot.
• 475 (5xx): TVMs, specials, and at least one pilot that was conceived as a TVM, beginning after the merger in a similar fashion and continuing for over a decade.
• 445-447, 455: Episodes from 89 onward, after the merger. This is the start of the main sequence of code prefixes that would go for about a decade before switching numbers. Each prefix applied to approximately one season's worth of episodes, with each show getting a 50-code block starting at 01 or 51 (thus up to 20 blocks). The third-digit rule dictates the pattern and moves through the first two digits very quickly. In these early years, some shows throw hyphens in (Miller-Boyett's Full House and The Hogan Family are the only ones I've seen with a 2-4 digit split, all others being 3-3) but quickly drop them.

Eight Is Enough	76-77	77-78	78-79	79-80	80-81	81-82	82-83	83-84	84-85	85-86	86-87	87-88
	770220 188351	188366	188651	188101*	189041								+
Dallas		188552	188566	188136	189002	189301	171101	172101	173101	174101 TVM ??	175101	176101	+
Knots Landing				790602 188817	189081	189402	171301	172301	173301	174301	175301	176301	+
Falcon Crest						189701	171201	172201	173201	174201	175201	176201	+
Valerie/Valerie's Family: The Hogans/ The Hogan Family										201037 174601	175601	176601	+
Perfect Strangers										174901	175501	176501	+
Full House												??????	+

		88-89	89-90	90-91	91-92	92-93
Eight Is Enough (TVM, 89)	^		475507
Dallas	^	177101 to 07 445008 to 26	445601 to 06 445607	446151			+
Knots Landing	^	177301 to 14 445115 to 28	445701	446201	446801	447751
Falcon Crest	^	177201 to 08 445059 to 72	445651
The Hogan Family (season 4+)	^	177601 to 13 445264 to 75	445801 or split*	446351 44-6356*
Perfect Strangers	^	177507 to 26 445227 to 28	445751 to 52 445753	446301	446851	447951
Full House	^	??????	44-5851	44-6401	446951	447851	+
Paradise/ Guns of Paradise		?????? 187101 to 12 445463 to 76, 55*	445951 or split*	446701
Nearly Departed		187201 to 06
Family Matters			445230* 446001	446451	446901	447801	+
DEA/ DEA: Special Task Force				475035 446651
The Family Man				475040 446051
Gabriel's Fire/ Pros and Cons				475034 446601	447301
Going Places				446501
Sisters				475039* 446751	447251	447651	+
Rewrite for Murder					475051
Step by Step					475049 447-001	447901	+
Homefront					447151	447701
Up to No Good					475048?
Hangin' with Mr. Cooper						475060 455001	+
Shaky Ground						455101
Time Trax						??????	+
Getting By						455251	+

Table 12A/B: Lorimar before 93, through the WB merger and start of onscreen codes.
*I have only a few scraps of info on Eight Is Enough season 4 codes, but they jibe with that year's pattern in Dallas.
*Paradise season 1 codes switch to the new system midseason, but it appears that episode 187105 was held back and became renumbered as episode 445455. I have not been able to find any season 1 credits but the codes are probably not seen.
*Paradise and The Hogan Family are 89-90 shows I've been unable to examine for the precise moment codes began to appear, but 60 (episode 10) is the lowest onscreen Paradise I've confirmed, and just the tail end of Hogan for now. The last half season of The Hogan Family also adds a hyphenation with a 2-4 split, starting by episode 56 (6th episode) but maybe one episode earlier. Updates to come.
*Family Matters is a spinoff of Perfect Strangers and, if the numbers can be believed, its pilot is of the backdoor variety, using a code from PS season 4's sequence (with a one-episode gap). Well, semi-backdoor: it aired as a Family Matters episode even if it wasn't quite produced as one.
*The Sisters pilot on DVD has no credits beyond main cast, and thus no onscreen code. Its presentation is like a not-for-air version, but it's hard to imagine it was broadcast like that. I'd love to see how it actually aired!

93-04: more six-digit numbers

For the fall of 93, Lorimar copyright and branding is gone, and all shows are fully WB. At the same time, codes finally appear onscreen for WB shows, and apart from a few leftovers from the old system they are all in the Lorimar style (or is it a WB style that only Lorimar actually adopted at first?). Some new sequences are introduced as well. There are some stragglers and apparent breaking-in confusion, such as a few unseen codes (Kung Fu: TLC and Brisco County, see table) and duplicated episode codes (Murphy Brown and Brisco County seem likely, for example, but I won't belabor them).

• 187, 206: The last vestiges of the old WB episode and pilot sequences, including the last block of less than 50. It's nice to see them onscreen as proof of the old system! This 187 is not to be confused with the brief Lorimar use of 187s in 88-89.
• 475 (0xx-2xx), 475 (5xx): Same as above, pilots and TVMs/specials. The latter sequence seems to fizzle out around 2000, with other prefixes taking up that purpose.
• 475 (3xx): A parallel, slower sequence of pilots (95-04) which I do not yet see the common trait of.
• 455-7, 465-7: Episodes as above, roughly one season to a prefix. Some sporadic hyphens bisect codes, usually in a consistent fashion per show, and this applies to some pilots and the next few sequences. These prefixes last until about 99. Those paying attention might notice that the next prefix in this pattern would be 475, which was already in use. What should come next? 476? 485?
• 225-7: Episode sequence for about 99-02. Why?
• 175-7: Episode sequence for about 02-04/05. This seems to be related to the 83 skip from 167 to 185, as if while scrambling for available codes someone settled on these (and ignored Lorimar's use of them in the 80s). And they would be some of the last all-numeric codes of all. But it's quite a baffling series of steps backward, isn't it?
• 296 (6xx-7xx): Special codes for various purposes, probably introduced around 93 in the low 600s (maybe even earlier). No part of the prefix or starting point seems based on anything (except maybe 206 for old pilots), although again it does follow the third-digit rule. These productions are generally side projects that seem to be WB-adjacent, with copyright holders/production company names like Lakeside and Riverside (among others), and they include TVMs/specials, pilots (whose series get "real" WB codes when picked up), and a few shows with whole seasons using a six-digit code for a base (see footnotes on Time Trax and Whose Line below).
• 236: One of a few offshoot prefixes I've not found more than one example of, but the beefiest and most related one. The 001 block belongs to The Oblongs, which has its own company name and was produced around the time 226 codes were being assigned (with some delay for animation), so it seems plausible that someone wanted to assign a similar-but-separate code. It's also the only animated WB-ish show I've found with codes (Animaniacs sequential numbering aside). I'll keep my eyes peeled for more. See also footnotes at Lucky (possible similar case) and Under Suspicion for some odd exceptions.

	93-94	94-95	95-96	96-97	97-98	98-99	99-00	00-01	01-02	02-03	03-04
LORIMAR CONT.
Dallas (TVM, 98)					296644
Full House	455-401	456-251
Family Matters	455351	456201	457101	465301	466451
Sisters	455851	456501	457001
Step by Step	455-451 455464*	456351	457151	465351	466501
...Mr. Cooper	455551	456401	457251	465601
Time Trax	296609-23*
Getting By	455501
WARNER BROS. CONT.
Dukes/Hazzard (TVMs, 97/00)				475521			475524
Murphy Brown	455901	456151	457051	465151	466651							*
Kung Fu: TLC	187571 187572	1001*	2001*
WARNER BROS. NEW
Living Single	475074 455751	456551	457351	466001	466851
Tall Hopes	206813 45600x
Brisco Cty. >	?????? 455951	Full title: The Adventures of Brisco County, Jr.
Lois & Clark >	475512 455301	456451	457401	465201	Full title: Lois & Clark: The New Adventures of Superman
Café Amer. >	475070 455801	Full title: Café Americain
Family Album	475072 455701
Walt. >	475514*	475516		475519	The Waltons (90s TVMs*)
On Our Own		475082 456301
Under Suspicion		296620* 29105x*
ER		475079 456601	457201	465401	466351	467551	225451	226251	227251	175151	176001	+
Friends		475085 456651	457301	465251	466601	467651	225551	226401	227401	175251	176251
The Wayans Bros.		456851	457701	466101	466401	467951
Hope & Gloria		456951	457751
Kirk			457-451	465951
The Drew Carey Show			475095 457501	465901	466251	467501	225401	226351	227301	227951	176551
Dweebs			475311 457801
Too Something/ New York Daze			475??? 457-851
High Society			465051
The Show			465101
Nick Freno: Licensed Teacher				475100? 465701	466701
The Jamie Foxx Show				475314 465801	466801	467701	225351	226451
Party Girl				4????? 465451
Lush Life				475106 465501
Suddenly Susan				465-751	466-301	467-351	225-501
Mr. & Mrs. Smith				296641 465851
Veronica's Closet					475128 466201	467901	225601
Prey					467051*

	93-94	94-95	95-96	96-97	97-98	98-99	99-00	00-01	01-02	02-03	03-04
Whose Line Is It Anyway?						296648 -101* 296717 -108*	296718 -201*	296722 -301* 296731* 296733 -340*	296734-401*    296735-501*       296736-601*			+
Jesse						475141 467401	225751
Vengeance Unlimited						475139 467851
The Norm Show/ Norm						475150 225151	225801	226601
Katie Joplin							225001
The West Wing							475151 225901	226201	227201	175301	176051	+
Third Watch							225301	226301	227701	175201	176751	+
Odd Man Out							475328 225851
The Strip							?????? 226001
Opposite Sex							475153 225951
Gilmore Girls								226730 226701	227451	175001	176151	+
The Fugitive								475160 226801
Hype								475340 226901
Nikki								226-151	227-151
The Oblongs								236-001
Night Visions								296723 296730* 226501
Thieves									475166  227651
Off Centre									227551	175351
Smallville									475165 227601	175051	176201	+
Babylon 5 (00s TVMs*)									296737			+
George Lopez									475181 175101	175401	176351	+
Everwood										475350 175501	176101	+
Fastlane										475183 175751
What I Like About You										475-352 175-601	177-401	+
Without a Trace										475182 175651	176401	+
Wanda at Large										475357* 175801	177351
Lucky										247117* 175851
Nip/Tuck											475194* 176451* 176454	+
The O.C.											475197 176501	+
The Mullets											177100 177101
Run of the House											475-365 177-201
All of Us											475369 176901	+
Two and a Half Men											475215 176801	+
I'm with Her											475-213 177-001
One Tree Hill											475360 177501	+
Cold Case											475195 176701	+
Skin											475205 176301
The Stones											475200 177251
The D.A.											177701

Table 13: WB (and continued Lorimar) all-numeric codes, 93-04.
*Step by Step's season 3 codes drop the hyphen starting at the 15th episode in air order (455466), but it mixes up production order quite a bit, so for simplicity I'm listing the change based on lowest production number in each set. 65 has the hyphen, then 66 and up do not.
*Despite being a Lorimar production during the 90s, season 1 of Time Trax does not have codes onscreen, and I do not know what they should be. Season 2 (now WB, or a syndication wing) uses subcodes and is numbered 296609-23 to 296609-44, opting for a cumulative episode count. This could suggest season 1 is the same with 01 to 22 codes, but there are plenty of reasons not to assume this, including the way Whose Line codes work (see below).
*The 2018 revival of Murphy Brown is listed online with inconsistent codes that I'd like to verify, if I can, before listing here.
*The last two seasons of Kung Fu: The Legend Continues drop the 6-digit codes and do their own thing, or so it seems. I've seen only a few examples but they seem to suggest 4-digit codes starting at 1001 and 2001. More information would be very welcome!
*Although The Waltons was a Lorimar show, I have not been able to find codes for its original run (or 80s TVMs), though they would be quite welcome. Because the relevant codes I do have come from the 90s TVMs under WB, I'm starting the entry here. And the 93 TVM has something else right under its WB code: "MRI# 1L06F0" (quotes mine). What does that one mean? Finally, I must indicate that the TVM that led to the original show, The Homecoming: A Christmas Story, which is not from Lorimar but CBS, actually does have a code of 1310-1736-6990. This reminds me of MTM pilots but I don't think it's related. Another rabbit hole for another time.
*Under Suspicion's post-pilot prefix of 291 is the primary post-Lorimar exception to the third-digit rule and it's baffling. It is a Lakeside production (as many 296s are), and it's one of the earliest examples, so maybe a new sequence was under way before the third-digit police reined it in. Other notes: Early episodes are very hard to find, and whether it has a 51 or goes from pilot to 52 is unclear (mathematically it seems like the latter, but that is not common for this era). And the pilot code I only have from split screen text credits on a 95 rerun, where it seems to be longer: "296620 296705-01"! I want to interpret this as a second pass at the pilot (see some dual codes from 20th), or something, perhaps applying the Time Trax approach to give an alternative number, but the 296 sequence had not advanced nearly this far at the time, and all other episodes I've found use just the 291 codes. Any help, as usual, would be appreciated.
*Prey's first episode actually uses a 52 code in all copies I can find, as does its second. I have a hunch this is either a typo or reused credits.
*Whose Line Is It Anyway? (only the Drew Carey years with Riverside have codes) uses subcodes to let a single 6-digit production code cover an entire season at a time, with some exceptions. The codes in this table are the first of each subset, with the last three digits denoting season-episode number. Note that seasons 1 and 3 were extended (in particular, the initial order seems to have been a small trial run, judging by the airdate hiatus and sequence gap); the orders for season 2 and 4-6 either were made along with the season 1 and 3 extensions or happened during slow periods for this sequence. 296731 is a single "Best of" episode that kicked off season 3. There is no episode 112 (see note above). And air order for seasons 4-6 (and the tail end of 3) is very jumbled up, with episodes being moved forward or held back significantly, so they might as well be lumped together as their production schedule seems to suggest. There may also be some mistakes in onscreen codes, including a single frame in 612 where a different, older code appears!
*Night Visions had two stories in each hour, and each half hour had its own production code (to keep them straight, the credits even provided the titles next to the codes!). It also had two pilot stories (the 296 codes), which were originally meant to go together, although the second ran much later. I'm not sure whether the plan was always to pair stories up, but it could explain why both of those drew from the pilot sequence instead of one taking a regular episode code.
*Original episodes and TVMs of Babylon 5 were only distributed by WB and used their own basic onscreen codes (apart from the pilot), even after WB acquired the show late in its run. This may be because it was under the "Pay TV, Cable and Network Features" wing, but it still was there for 2002's The Legend of the Rangers, which got the special sequence number 296737. See also below.
*The 475 code for Wanda at Large is in some episode guides rather than the 01 code seen on the aired first episode. It may represent an unaired version of the pilot.
*The pilot code for Lucky uses a 247 prefix I've not seen elsewhere, vaguely similar to the contemporary 227 episode prefix, but the 117 suggests another side sequence waiting to be fleshed out. (It also lists the copyright under another company for all episodes.) But it follows the third-digit rule! And as with many other odd pilots, regular WB codes were used for the series.
*Nip/Tuck does not display codes for the pilot or the next three episodes, although a slate for episode 51 in the season 1 gag reel demonstrates that they were indeed being used during production. I can only suppose the omission was accidental, but it's a very rare accident (others have been on purpose or late in a transition).

04-14: the alphanumeric decade

For reasons beyond me, here letters infiltrate the all-numeric codes, specifically replacing the second digit on regular episode codes. At first it's just the letter T, but then others are introduced to mark spinoff sub-brands (Bonanza Productions and Horizon Scripted Television, the latter using a new end logo for Warner Horizon); these sequences have fewer productions and move more slowly. None of these letters have obvious meaning.

Beginning in fall 10, episode codes 01 and 51 are dropped for shows whose pilots air as episodes, and their post-pilot episodes start from 02 and 52, except for Horizon shows (shows with unaired or no pilots code normally).

• 177: Tail end of all-numeric episode codes (apart from pilots, etc.).
• 296 (7xx-8xx): Same as above, except it seems to be used just for Bonanza-produced pilots (see below) at the end, with the last example in 2014. See also footnote for 235.
• 475 (2xx): Tail end of pilot codes (through 06), presumably halting when it would run into the 300s that had already been used.
• 276: New pilot sequence (starting in 06 and lasting about a decade), using the popular first digit 2, perhaps to match the new alphanumeric sequences.
• 2T5-7: Episode sequence for about 04-07. The first alphanumeric codes in company history. These next few and the 276 pilots are used only for "full" WB shows. Hyphens drop out almost entirely, though the exception is amusing: while What I Like About You (the main holdout) responded by taking its hyphens out, Cold Case added them for the first time, as if the format change altered the perceived divisibility of the sextets in completely opposite ways!
• 3T5-7: Episode sequence for about 06-09.
• 3X5-7: Episode sequence for about 10-13. Did the letter change instead of the number because "4T" sounds like "forty" out loud?
• 4X5: Episode sequence for 13-14 (continued in next decade, but not for very long).
• 2J5-7: Episode sequence for Bonanza shows starting in 09 (matched with high 296 pilots).
• 296 (0xx): Pilot sequence just for Horizon shows (about 10-12 for the few I've seen).
• 2M5-6: Episode sequence for Horizon shows, probably starting in 09 too (matched with low 296 pilots).

04-05

05-06

06-07

07-08

08-09

09-10

10-11

11-12

12-13

13-14

ER

^

177851

2T6051

2T7801

3T6151

3T7101

Whose Line Is It Anyway?

^

296744 -7001*

296751 -8001*

The West Wing

^

2T5001

2T6201

Third Watch

^

177901

Gilmore Girls

^

2T5301

2T6301

2T7751

+

Smallville

^

2T5201

2T6401

2T7701

3T6301

3T7451

3X5251

3X6001

Babylon 5*

^

235024*

*

George Lopez

^

177801

2T7401

3T5201

Everwood

^

2T5051

2T6601

What/Like/You

^

177-951

2T6551

Without/Trace

^

2T5151

2T6101

2T7851

3T6101

3T7201

Nip/Tuck

^

177601

2T5951

3T5001

3T6401

3T7901 3T7960*

The O.C.

^

2T5101

2T6251

3T5251

All of Us

^

2T5651

2T7301

3T5851

Two/Half Men

^

177651

2T6501

2T7951

3T6251

3T7401

3X5501

3X6451

3X6951

3X7401

4X5351

+

One Tree Hill

^

2T5251

2T6151

3T5751

3T6801

3T7551

3X5301

3X6351

3X7201

Cold Case

^

177751

2T6-351

2T7-901

3T6-351

3T7-151

3X5-451

Joey

475246 2T5451

2T6451

The Mountain

475257 2T5351

Veronica Mars

475258 2T5701

2T7201

3T5801

+

Jonny Zero

?????? 2T580x

The Closer

475273 2T6001

2T7651

3T6051

3T7001

3X5001

3X5901

3X6551

Reunion

475282 2T6851

The War at Home

475294 2T7601

3T5601

Supernatural

475285 2T6901

3T5501

3T6901

3T7501

3X5201

3X6051

3X7051

3X7801

4X5051

+

Invasion

475281 2T6951

Close to Home

475234 2T6701

3T5951

Related

2T7051

Hot Properties

475293? 2T755x

Freddie

2T7191 2T7151

Four Kings

475280 2T7351

The New Adventures of Old Christine

475297 2T7451

3T5551

3T6701

3T7851

3X5601

Happy Hour

276005 3T5351

The Class

?????? 3T5151

Studio 60 on the Sunset Strip

276003 3T5051

20 Good Years

276??? 3T540x

Notes from the Underbelly

276011 3T5901

3T6651

Gossip Girl

276026 3T6751

3T7601

3X5151

3X5951

3X6601

3X7651

*

Chuck

276025 3T6451

3T7251

3X5801

3X6301

3X6751

The Big Bang Theory

276018* 276023 3T6601

3T7351

3X5551

3X6651

3X6851

3X7601

4X5301

+

Moonlight

3T6951

Pushing Daisies

276027 3T6501

3T7051

Terminator: The Sarah Connor Chronicles

276022 3T6851

3T7301

Fringe

276038 3T7651

3X5101

3X6101

3X7001

3X7501

Privileged

3T7791 3T7751

The Mentalist

276040 3T7801

3X5351

3X6401

3X6801

3X7951

4X5601

+

Southland

276046 3X5051

3X5751

3X6151

3X6701

3X7551

The Vampire Diaries

296766 2J5001

2J5251

2J6001

2J6651

2J7501

+

The Middle

276032* 276047 3X5701

3X6501

3X6901

3X7451

4X5501

+

V

3X5441 3X5401

3X6201

Rizzoli & Isles

296014 2M5451

2M5601

2M5901

2M6251

+

Hellcats

2J5591 2J5552

Nikita

276051 3X6252

3X7151

3X7351

4X5251

Mike & Molly

296772 2J5852

2J6501

2J6751

2J6851

+

Better with You

296777 2J5802

Harry's Law

2J5901

2J6101

Shameless

296769 2J5402

2J5951

2J6601

2J7751

+

2 Broke Girls

296793 2J6352

2J6701

2J6801

+

Person of Interest

296807 2J6202

2J7201

2J7601

+

Dallas

296021 2M5801

2M6151

2M6401

Major Crimes

3X7251

3X7901

+

Revolution

296830 2J7102

2J7701

Mom

276061 4X5402

+

The 100

296843 2J7052

+

Table 14: WB six-character codes with letters, 04-14.
*Whose Line Is It Anyway?: See note above. For the more self-contained seasons 7 and 8, the episode subcodes are oddly 4 digits instead of 3.
*The 2007 B5 Voices in the Dark is actually straight-to-DVD and not quite a TVM, and it bears this code with a 235 prefix not seen elsewhere (I have not been looking hard for this sort of material). Once again, it follows the third-digit rule and starts with a 2, and the low code number suggests a side sequence of recent origin (perhaps around the time of 2T5) or an older, infrequently-used one. The 2023 animated The Road Home has no code, but it's also from the WB Animation department so this is not a surprise.
*After Nip/Tuck's season 5 was stretched out into half seasons a year apart, its final season was merged from two. The first 9 episodes are 3T7901 to 09, and the last 10 are 3T7960 to 69. Wikipedia indicates that the last 9 were meant to be a 7th season to air the next year, and that even when they were merged into season 6 they were occasionally referred to as separate seasons with just a few weeks in between. That all makes sense, and even the adjacent code blocks could be explained if both short seasons were ordered at the same time. It's interesting that the second half's codes were offset to create continuity (see also The Leftovers) and I have to assume that codes were contractually bound to stay in the new block (see early 90s WB code scrounging). But these numbers suggest 9+10, not 10+9! Why isn't it 01-10 and then 61-69?
*A 2021 reboot of Gossip Girl uses only codes like 101, despite being WB (in conjunction with CBS). Go figure. xoxo
*The first codes listed for The Big Bang Theory and The Middle are unaired pilots, in contrast to the later-numbered versions aired as their first episodes. It's a neat look at the process of occasionally revising and reselling a show. See also next section.

Below is one more short list, a set of unsold pilots for extra comparison (including a few that technically belong in the previous or next period). Most of these are culled from sales versions with info slates but no credits, most dated in the spring before their intended broadcast season. These were not picked up and it does not seem any aired, but if I learn any did, I will move them. See also unaired early pilots of The Big Bang Theory (276018, series began fall 07) and The Middle (276032, dated spring 07 though series began fall 09).

Spring 03+	111 Gramercy Park	475-202	Two versions; second likely from 2004 but WB web release is © 2008
	Gramercy Park	475248
Spring 04	Hot Mama	475-247
Fall 04	Rocky Point	475373	Secondary 3xx sequence
Spring 05	True	475277
	The Studio	475289
Spring 06	Separated at Worth	276020	a.k.a. The Sisters Project
	Jungle Gym	276012	Episode title "Welcome to the Jungle Gym"
Spring 10	Edgar Floats	296773	Bonanza; episode title "Your Own Personal Judas"
	Nolan Knows Best	296782	Bonanza
Spring 12	The Selection	296828	Bonanza
	Wicked Smart	276058	a.k.a./episode title "Prodigy"/"Bully"?
Spring 14	Dead Boss	276078

Table 15: WB unsold pilot codes, 03-14.

14-present: a spot of T for U

Over a few seasons, the six-character codes are phased out and replaced by a lengthier but perhaps more robust, yet almost equally inscrutable, system. The fascinating decision to double up old and new code styles allows for a little continuity and examination of how they correspond. The main change is from the three-character prefixes to five-character (plus a period) ones that make the type and sequence more distinct: a letter (T, maybe for television?, except for U for Horizon presumably to maintain a quota of nonsense), a two-digit number to identify a sub-brand or company, a period, and a two-digit number that increments as prefixes did. Code blocks are still assigned in the same way, though the rollover from third-to-last digit to fourth-to-last is a little clearer now. Still, the change seems to have lost something appealing along the way.

Some T numbers seem to indicate coproductions with other studios (such as Universal and even 20th), but codes are all WB style. Other numbers seem to be doled out for separate production wings, which I won't enumerate. The major sequences seem to have been in place for some time, and all may have begun at .10 (xxx), but working backward from equivalent codes suggests no consistent starting point.

Description of current shows is, as usual, a little sparse and unconfirmed (not helped by streaming siloing). Other patterns and developments may become clear as the new system goes on, and more information is welcome. The use of 50-episode blocks (specifically episode codes starting at 51) may be on the way out, especially among the splinter sequences.

• 276: Tail end of 6-digit pilot codes. Any high or low 296 codes from this period are not known to me yet.
• 4X5-7: Tail end of 6-character episode codes in main sequence.
• 2J6-7, 3J5-6: Tail end of 6-character episode codes for Bonanza shows.
• 2M6-7: Tail end of 6-character episode codes for Horizon shows.
• T11.10 (1xx): Pilot codes for new main sequence (shows take T12 prefixes). No hybrids spotted yet but given T15 behavior seems unlikely to be a continuation of 276 sequence.
• T12: Episodes in new main sequence (hybrids: T12.14=4X6, T12.15=4X7).
• T13: Episodes in new secondary sequence (hybrids: T13.18=4X5, T13.19=4X6 and one high 4X7, see below). Many but not all of these shows list the owner as "NS Pictures".
• T15.10 (1xx): Pilot codes for new secondary sequence T13 (hybrid: T15.10117=276083 without numeric correspondence).
• T26: Episodes in one very slow new Bonanza sequence (hybrids: T26.10=2J6, T26.11=3J5 and 3J6 with no collisions), may have ended by 17.
• T27: Episodes in another new Bonanza sequence (hybrids: T27.11=2J7, T27.12=3J5, T27.13=3J6), may have ended by 21.
• U13: Episodes in new Horizon sequence (hybrids: U13.11=2M6, U13.12=2M7). No separate pilots spotted yet, and as of about 2021 the Horizon branding has been dropped for yet another version of the WB name (Warner Bros. Television Production, barely distinct from others).
• T numbers not listed above: Miscellaneous production companies and/or coproductions with no clear pattern. The T numbers are high, but the sequences are very low-numbered, some with separate pilot sequences, none so far with codes starting in the 50s.

		14-15	15-16	16-17	17-18	18-19
Gilmore Girls	^			4X7701
Two and a Half Men	^	4X6951/T12.14951
Veronica Mars	^					T13.21601
Supernatural	^	4X5801/T13.18801	4X6251/T13.19251	T13.19951	T13.20551	T13.21151	+
Big Bang Theory	^	4X6751/T12.14751	4X7201/T12.15201	T12.15301	T12.15601	T12.16001
The Mentalist	^	4X5951/T13.18951
Vampire Diaries	^	2J7851/T27.11851	3J5701/T27.12701	T27.13301
The Middle	^	4X6601/T12.14601	4X7101/T12.15101	T12.15251	T12.15651
Rizzoli & Isles	^	2M6551	2M6951/U13.11951	2M7251/U13.12251
Mike & Molly	^	3J5001/T26.11001	3J6101/T26.11101
Shameless	^	3J5101/T27.12101	3J5851/T27.12851	T27.13051	T27.13501	T27.13701	+
2 Broke Girls	^	2J6901/T26.10901	3J5051/T26.11051	601/T26.11151
Person of Interest	^	3J5401/T27.12401	3J6001/T27.13001
Major Crimes	^	4X5751 4X5767/T13.18767	4X6101/T13.19101	4X7751/T13.19751	T13.20451
Mom	^	4X6701/T12.14701	4X7051/T12.15051	T12.15351	T12.15701	T12.16101	+
The 100	^	3J5251/T27.12251	3J5751/T27.12751	T27.13251	T27.13551	T27.13801	+
The Leftovers		276070 4X5702	4X6051/T13.19051	T13.19801  T13.20203*
Stalker		?????? 4X590x/T13.1890x
Fuller House			2M7051/U13.12051	2M7451/U13.12451	U13.12801	U13.13301	+
Westworld				276083/T15.10117 4X6152/T13.19152	201		+
Young Sheldon					T12.15551	T12.16051	+
You						U13.12901	+
All American						T15.10151 T13.21352	+
Titans						T15.10146 T13.20902	+

		19-20	20-21	21-22	22-23	23-24	24-25
Supernatural	^	T13.21751
Shameless	^	T27.13901	T27.14101
Mom	^	T12.16401	T12.16601
The 100	^	T27.14051
Fuller House	^	U13.13901
Westworld	^	301		401 402
Young Sheldon	^	T12.16451	T12.16751	T12.17201	T12.17701	T12.18701
You	^	U13.13701		U13.14301	U13.14801		U13.15501
All American	^	T13.22201	T13.22501	T13.23401	T13.24501	T13.24601	T13.24701
Titans	^	T13.21651		T13.22451*	T13.23551*
Bob Hearts Abishola		T11.10127 T12.16502	T12.16701	T12.17301	T12.17801	T12.18501
All Rise		T15.10156 T13.22102	T13.22801		T13.23651
Prodigal Son		T88.01001 T88.10102	T88.10201
Stargirl			T56.10101	T56.10201	T56.10301
B Positive			T11.10137 T12.16802	T12.17251
Superman & Lois			T13.22401	T13.23251	T13.24051		T13.24401
United States of Al			T11.10132 T12.16902	T12.17351
Kung Fu			T13.22851	T13.23351	T13.23951
Lisey's Story			T64.1010x
The Waltons (reboot TVMs)				T62.10001	?????
Abbott Elementary				T11.10144 T12.17152	T12.17551	T12.18301	T12.19401
All American: Homecoming				T13.23501	T13.24201	T13.24301
The Winchesters					T15.10162 T13.24102
Found						T74.10005 T74.10102	T74.10201
Presumed Innocent						T13.23851
Bad Monkey							T82.10301
Rescue: HI-Surf							T59.10101
Georgie and Mandy's First Marriage							T12.19101

Table 16A/B: WB transitional six-character and T codes, 14+.
*The Leftovers filmed in Australia for the bulk of season 3 after beginning in Texas, and it seems this was enough of a change to use two production blocks, with only 01 and 02 coming out of the first one, and numbering resuming at 03 in the next (see also Nip/Tuck).
*Season 3 and 4 codes for Titans are followed by "(SAP)", and I'm stumped. It could have something to do with the giant ACTRA logo that appears starting then, but so far I'm turning up nothing, and it's a bit confusing when SAP already has a meaning in TV (second audio program in a broadcast, often another language or descriptive track, though one would expect any notations about alternative audio to be somewhere else in the credits). My source is a standard English DVD.