Retroactive continuity

Retroactive Continuity, also known as retcon, is the phenomenom of dealing with continuity errors in fiction after the fact. Retcon can consist of something as simple as a character claiming to have misspoken or as involved as the artist wishes to make it, including twins, alternate timelines and vast conspiracies.

The Doctor Who universe, having been created by hundreds of writers, actors, directors, comic artists and novelists over the course of (currently) almost eight hundred TV episodes, thousands of novels and shorts stories, and uncounted comic strips, is susceptible to continuity errors. The refusal of the BBC to declare which works are canon creates confusion and controversy.. Efforts at retroactive continuity are a constant source of fan discussion.

One of the most frequently discussed continuity errors in the Doctor Who universe is probably the UNIT dating controversy, although many of the facts about the Doctor, including his age and his family are also ripe subjects for retcon.