Retroactive continuity

Retcons sometimes do not contradict previously established facts but instead fill in missing background details, usually to support current plot points. Thomas referred to "retroactive continuity" in this sense, as a purely additive process that did not undo any previous work; such additions were common in All-Star Squadron. Kurt Busiek took a similar approach with Untold Tales of Spider-Man, a series which told stories that specifically fit between issues of the original The Amazing Spider-Man series, sometimes explaining discontinuities between those earlier stories. John Byrne used a similar structure with X-Men: The Hidden Years. Possibly the earliest Marvel Comics example of new stories placed between long-established stories was the 1977-8 magazine The Rampaging Hulk. In The Godfather Part II, the character Frank Pentangeli is introduced as an old friend of the family though he is not referenced in the first movie; similarly Don Altobello is one of the "old time" Dons, though he is not mentioned until The Godfather Part III. Neither addition affects the plot line of the previous films. The addition, in later seasons, of an attic to the family's home in Full House stands as a similar additive example.

A similar concept is that of secret history, in which the events of a story occur within the bounds of already-established events (especially real-world ones), revealing different interpretations of the events. Some of Tim Powers' novels use secret history, such as Last Call, which suggests that Bugsy Siegel's actions were due to his being a modern-day Fisher King.

Alan Moore's additional information about the Swamp Thing's origins – revealing that Swamp Thing was not actually scientist Alec Holland converted into a plant, but actually a plant that had absorbed Holland's body and consciousness so that it merely thought it was Holland – did not contradict or change any of the events depicted in the character's previous appearances, but instead changed the reader's interpretation of them. Such additions and reinterpretations are very common in Doctor Who.[3]

In the Star Wars franchise, one of the most cited plot holes is that the Galactic Empire's superweapon, the Death Star, has a glaring, poorly defended weak point: an exhaust port. However, the movie Rogue One: A Star Wars Story, which acts as a direct prequel to A New Hope, presents the design flaw as deliberate: Galen Erso, the head engineer of the Death Star project, designed the reactors to be unstable, thus needing an exhaust port, and gave the plans to the Rebel Alliance in order to sabotage the Empire and to secretly show the Rebels how to destroy the Death Star.

Retcons sometimes add information that seemingly contradicts previous information. This frequently takes the form of a character who was shown to have died but is later revealed to have somehow survived. This is a common practice in horror films, which may end with the death of a monster that goes on to appear in one or more sequels. The technique is so common in superhero comics[3] that the term "comic book death" has been coined for it. An early example of this type of retcon is the return of Sherlock Holmes, whom writer Arthur Conan Doyle apparently killed off in "The Final Problem" in 1893,[9] only to bring him back, in large part because of readers' responses, with "The Empty House" in 1903. Another example is the character Phil Coulson, who was killed off in the Marvel Studios film The Avengers (2012), but is later shown to have survived in the television series Agents of S.H.I.E.L.D.

In many of his detective novels, Rex Stout implies that his character Nero Wolfe was born in Montenegro, giving some details of his early life in the Balkans around World War I. But in 1939's Over My Dead Body, Wolfe tells an FBI agent that he was born in the United States. Stout revealed the reason for the change in a letter obtained by his authorized biographer, John McAleer: "In the original draft of Over My Dead Body Nero was a Montenegrin by birth, and it all fitted previous hints as to his background; but violent protests from The American Magazine, supported by Farrar & Rinehart, caused his cradle to be transported five thousand miles."[10]

In the 1940s and 1950s, Isaac Asimov placed the planet Trantor, capital of the Galactic Empire, at the "center of the galaxy", but later astronomical research indicated that the actual Galactic Center might be occupied by a supermassive black hole, making human life there impossible; in later works, Asimov adjusted his galaxy and Trantor's location in it.

When E.E. "Doc" Smith wrote the original The Skylark of Space, space flight was a completely theoretical proposition. However, the last book of the series, Skylark DuQuesne, was written in 1963, when the United States and the Soviet Union were involved in the space race. Smith adjusted the past of his series accordingly, mentioning an American base and a Soviet one being established on the Moon prior to the protagonist Seaton discovering faster-than-light flight.

Alan Moore's retcons often involve false memories. He has used this technique in the Marvelman series, Swamp Thing and Batman: The Killing Joke.

Retconning can bring back characters who were initially killed off. An example of this occurs on the CBS comedy Two and a Half Men. The character Charlie Harper (Charlie Sheen) was killed in a train accident and briefly returns as a ghost (played by Kathy Bates) in the ninth season. Despite numerous instances that confirm his demise including the fact that a mutilated body was in his coffin, the season twelve series finale "Of Course He's Dead", it is revealed that Charlie survived the ordeal and has been held captive against his will for over four years. It is mentioned that there was no body only random body parts. It is also common in soap operas. On The Bold and the Beautiful, Taylor Forrester (Hunter Tylo) was shown to flatline and have a funeral. When Tylo reprised the character in 2005, a retcon explained that Taylor had actually gone into a coma.

The TV series Dallas annulled its entire Season 9 as being just the dream of another character, Pam Ewing. Writers did this to offer a supposedly plausible reason for the major character of Bobby Ewing, who had died onscreen at the end of Season 8, to be still alive when actor Patrick Duffy wanted to return to the series. This season is sometimes referred to as the "Dream Season" and was referred to humorously in later TV series such as Family Guy.

In Star Trek II: The Wrath of Khan, the character of Spock dies in the film. This was done because actor Leonard Nimoy would not agree to appear in the film unless the character was killed off. After the film was finished, Nimoy told producers he enjoyed making the movie and wanted to return if a third Star Trek film was made. As a result, an epilogue was added to the film, hinting at the possibility of Spock's resurrection.

Also in Star Trek II, the characters of Khan (Ricardo Montalbán) and Pavel Chekov (Walter Koenig) remember each other from Khan's appearance in the first season Star Trek television series episode Space Seed, 15 years earlier; The character of Chekov did not appear in Star Trek until the second season; It was later explained that Chekov was not a member of the Enterprise bridge crew at that time and was assigned elsewhere on the ship.

In Beverly Hills 90210, Kelly Taylor starts out in the first season initially not knowing Dylan McKay. Later when Brenda Walsh is sent to Paris with Donna Martin, Kelly Taylor has suddenly known him since kindergarten. This apparent retooling of the storyline contradicted years of prior character development and was apparently done to prepare viewers for Shannen Doherty's exit from the series.

Marvel Comics' Beyonder was originally stated to be omnipotent and the most powerful being in Marvel Universe, coming from the Beyond Realm. However, after his creator, Jim Shooter, left Marvel, writer-editor Tom DeFalco re-tooled the Beyonder, diminishing his power greatly: he was no longer omnipotent, as certain other cosmic entities were retroactively vastly upgraded to transcend the scale of infinity on which the character worked. Even after this, Beyonder was still one of the most powerful beings in Marvel, with several characters exceeding him.

In 2003, in the title of DC Comics' Teen Titans, Geoff Johns changed the entire genetic code of Kon-El (the modern version of Superboy) from a genetically altered human clone that was designed to be as Kryptonian as possible into a hybrid clone of both Superman and Lex Luthor. This change contradicted years of continuity and various facts that proved that Kon-El was human and in the process mostly ignored his unique ability of tactile telekinesis that made his powers very different from those of Superman.

In Boy Meets World, both Shawn Hunter and Topanga Lawrence have siblings in the first season but later in the series are retconned to be only children (though Shawn's half-brother Jack is introduced in later seasons). The ages of the characters of Boy Meets World are altered notably where Cory is age 11 in 6th grade during season 1 to age 13 and 7th grade in season 2. This happens again in high school skipping another grade. The age gap between Cory and Eric also narrows from 4 years apart in age to 2 years apart in age. Another prominent retcon during that series was that of the character of Morgan Matthews, who was portrayed by two actresses during the show's run; in the series finale of the sequel series Girl Meets World, the continuity suggests that they were two separate people who both appeared together for the only time during that episode.

Unpopular or embarrassing stories are sometimes later ignored by publishers, and effectively erased from a series's continuity. Later stories may contradict the previous ones or explicitly establish that they never happened.

A notable example of subtractive retconning is the X-Men film series. The 2014 film X-Men: Days of Future Past features the character Wolverine traveling in time to 1973 to prevent an assassination that, if carried out, would lead to the creation of a new weapons system called the Sentinels that threatens the existence of mutants — and potentially, all of humanity.[11] The events of this film retconned those of two previous films in the series:

• X-Men: The Last Stand (2006)

The film, a loose adaptation of "The Dark Phoenix Saga" from the Uncanny X-Men comic book series, featured the unceremonious deaths of select key characters (including Cyclops), triggering a mixed fan response from those who felt the deaths were sudden and under-explored. Days of Future Past erased these deaths and the characters are shown to have survived at the end of the film. "The Dark Phoenix Saga" would subsequently be adapted a second time in Dark Phoenix (2019).

• X-Men Origins: Wolverine (2009)

The film featured the character Deadpool, who is created by the character Colonel William Stryker as an amalgamation of several other mutants. He is referred to as "the Deadpool" due to having the other mutants' abilities "pooled" together. This version of the character was poorly received by fans due to his appearance and origin, both of which were considered unfaithful to the comics version of the character. The events of Days of Future Past allowed a more faithful version of the character to be adapted in Deadpool (2016) and its 2018 sequel, both of which were positively received by fans and critics.

An unpopular retcon may itself be retconned away, as happened with John Byrne's Spider-Man: Chapter One.

Film sequels often employ temporal compression to maintain a sense of urgency in each installment, despite more time having elapsed diegetically ("in-universe") between one installment and another than has elapsed in the real world. For example, despite the implied contemporaneity in each of the films of The Omen series, the lead character ages some 15 or 20 years across three films released over a period of less than 6 years.