Forum:Doctor Who television discontinuity and plot holes/Major inconsistencies and retcons

Doctor Who Universe stories have had a number of inconsistencies as well as deliberate retcons.

Overview
In the course of a history lasting more than forty-five years, hundreds of stories set in the Doctor Who Universe stories have been created in many different media. Inevitably, there have been occasions where the programme has contradicted itself. This was sometimes due to one production team simply not being aware (and often not really caring) of what had previously been shown on screen, but also occasionally the result of a deliberate attempt to rewrite or "retcon" away old continuity.

As an example, Terrance Dicks and Malcolm Hulke believed that a previous mention of "Time Lords" had appeared when they set about writing The War Games, when the series had never done so before. By mistake, they ended up creating the concept.

A major and concerted attempt to retcon happened when the writing team assembled by Andrew Cartmel (Script Editor from Season 23 to Season 26) and writers Marc Platt and Ben Aaronovitch, attempted to make the Doctor more mysterious and powerful again, and came up with a secret backstory for him known as the "Cartmel Masterplan", first hinted at in Remembrance of the Daleks and even more so in its novelisation. Doctor Who's cancellation in 1989 meant that this did not go very far.

In the 1990s many of the official Doctor Who stories that were released were written by fans of the programme who often attempted to address some of these 'inconsistencies' themselves, providing retcons where necessary.

Retcons are more common in material other than the television series proper, but these stories also contain some of the most blatant inconsistencies. Ace, for example, has been given numerous different fates in different media which fail to match up with each other.

The Doctor
Later: The Doctor stole his TARDIS. (DW: The War Games) ''The First Doctor often boasted and this might have him just trying to impress his human companions. It's also possible he did build the TARDIS, but later stole it.''
 * Originally: The Doctor built his TARDIS.

Later: The term TARDIS is in wide use among the Time Lords (DW: The Deadly Assassin, et al). However, the televised series has never directly contradicted the possibility that Susan did coin the term.
 * Originally: Susan Foreman devised the TARDIS acronym (DW: An Unearthly Child).

Later: The Doctor has two hearts. (DW: Spearhead from Space) While MA: The Man in the Velvet Mask claims Time Lords acquire their second heart only after their first regeneration, the revived series has established that serious injury or trauma can cause one of a Time Lord's hearts to stop beating. (DW: The Christmas Invasion, The Shakespeare Code) 
 * Originally: The Doctor has one heart. (DW: The Edge of Destruction)

Later: The Eighth Doctor describes himself as half-human. (DW: Doctor Who (1996)) ''Every Doctor has been unstable and more eccentric than usual after regeneration. His claim to be half-human on his mother's side might have been a manifestation of this instability, or it might just have been a joke. Although the TV series itself has yet to address the issue directly, spin-off media have done so, with IDW: The Forgotten establishing that the "half-human" statement was a deliberate ruse and BFA: The Apocalypse Element establishing that the "half-human" element of the Eye of Harmony identified in the film was due to an earlier incident involving Sixth Doctor companion Evelyn Smythe having her eyeprint "programmed" into the Matrix. In the televised episode Journey's End, a half-human clone of the Doctor is created and is disturbed by this unprecedented condition.''
 * Originally: The Doctor has a fully alien (or as later explained, Gallifreyan) ancestry.

Later: The Doctor and Sarah Jane never met again after her departure in what was thought to be South Croydon (DW: School Reunion), until she encountered him in his tenth incarnation. ''It's possible to rationalize that, due to the paradoxes involved, the Doctor and Sarah Jane had their memories of the Five Doctors adventure erased or suppressed. There's also the fact that her only substantial interaction in that story was with the Third Doctor.''
 * Originally: The Doctor, during his fifth incarnation, met three of his four prior incarnations during an incident on Gallifrey, as well as past companion Sarah Jane Smith. (DW: The Five Doctors)

Later: In DW: Aliens of London the Ninth Doctor says he is 900 years old, and in DW: Voyage of the Damned, the Tenth Doctor gives an exact age of 903. A reason for this change of the Doctor's age has yet to be suggested in any episode or licensed spin-off media.
 * Originally: The Doctor states that he is 953 years old soon after the start of his seventh incarnation. (DW: Time and the Rani)

The Time Lords
Later: Time Lords have a set number of regenerations, which heavily implies that Time Lords have a finite lifespan. (DW: The Deadly Assassin) ''Time Lords don't die of old age or natural causes; a Time Lord could still live forever if he or she didn't have an accident in their final incarnation. Also the Doctor has never died from anything other than 'an accident.' His first regeneration may have been due to his body aging rapidly, or his life force drain, so his body was biologically unstable. Also, from a human perspective, the ability to live 900, 1,000 years or more is effectively "forever".''
 * Originally: The Time Lords can, as the Second Doctor said, "live forever, barring accidents". (DW: The War Games)

The Daleks
Later: The Daleks were the result of mutation from the fallout of a thousand-year war coupled with the genetic manipulation of the scientist Davros. (DW: Genesis of the Daleks) The revived series, and to a degree the original series, have strongly suggested that alterations in the timeline have occurred that may have altered the course of Dalek history.
 * Originally: The Daleks were the mutated survivors of a war fought using a neutron bomb.

UNIT

 * See the UNIT dating controversy.

The Doctor

 * The Sixth Doctor regenerated after his TARDIS was struck by the Rani's tractor beam. (DW: Time and the Rani)

Retcon: The (unborn) Seventh Doctor 'kills' the Sixth Doctor to bring himself into being. (NA: Timewyrm: Revelation, NA: Head Games)

Further retcon: The Doctor was already dying when the TARDIS came under attack. (PDA: Spiral Scratch)

The Daleks
Retcon: The Doctor had destroyed the planet Antalin, rather than the real Skaro. (EDA: War of the Daleks) The apparent contradiction of Skaro appearing in Doctor Who (1996) after it was destroyed in Remembrance of the Daleks is easily explained if the Master's trial took place before that destruction.
 * The Seventh Doctor destroyed Skaro. (DW: Remembrance of the Daleks)