In the 5th episode of 1975 story "Genesis of the Daleks", Davros threatens to torture Sarah and Harry unless the (4th) Doctor gives information about Dalek losses. I assume that there was some means of telling whether the Doctor was being honest or, otherwise, it would have been pretty pointless.
Under interrogation the (4th) Doctor states that the Daleks were defeated on Earth in the year 2000 and the conversation tails off as he mentions "release of magnetic properties".
Of course, in the 1964 TV serial "The Dalek Invasion of Earth" the date of the invasion was given as 2164. As well, the reason for the Dalek failure was by the setting of off an active volcano, the Dalek saucer being caught in the explosion rather than the release of magnetic energy (this was the explanation given in the 1966 film version "Daleks Invasion Earth: 2150 AD").
In the final scenes of Genesis, the Doctor notes that the Daleks have been "delayed by perhaps a thousand years".
Two related questions: (1) Was the 4th Doctor's 2000 date was in some original time line, which changed because of his actions delaying the Daleks, or just poor continuity checks? (2) Was the comment about "magnetic properties …" influenced by the film or rather, again, poor continuity checks?