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

On some instances we have simply gotten informed of previously vague information. We have learned for example, the name of the the Doctor's people. On other occasions, the Doctor Who Universe has often contradicted itself and on some occasions, however, major retcons have occured that have changed our understanding of the universe. This list includes only changes that directly changes what we knew before, rather than new information that only fills in information. Some of these retcons have provoked major controversy amongst fans.

The Doctor
Retcon: The Doctor stole his TARDIS. (DW: The War Games)
 * The Doctor built his TARDIS.

Retcon: The Doctor has two hearts. (DW: Spearhead from Space)
 * The Doctor has one heart. (DW: The Edge of Destruction)

Retcon: The Doctor has had a number of incarnations prior to the First Doctor. (DW: The Brain of Morbius)
 * The Doctor has not had incarnations prior to the First Doctor. (DW: The Three Doctors)

Retcon: The Eighth Doctor describes himself as half-human. (DW: Doctor Who: The TV Movie)
 * The Doctor has a fully alien (or as later explained, Gallifreyan) ancestry.

The Time Lords
Retcon: Though this not directly contradict anything seen before, a later story portrayed the society of Time Lords as morally, intellectually and technologically decadent. (DW: The Deadly Assasin)
 * The Time Lords have a highly advanced and powerful civilisation. (DW: The War Games)

Retcon: Time Lords have a set number of regenerations, which heavily implies that Time Lords have a finite lifespan. (DW: The Deadly Assassin)
 * The Time Lords can, as the Second Doctor said, "live forever, barring accidents". (DW: The War Games)

The Daleks
Retcon: The Doctor had destroyed the planet Antalin, rather than the real Skaro. (EDA: War of the Daleks)
 * The Seventh Doctor destroyed Skaro.