"Day by day and almost minute by minute the past was brought up to date. In this way every prediction made by the Party could be shown by documentary evidence to have been correct; nor was any item of news, or any expression of opinion, which conflicted with the needs of the moment, ever allowed to remain on record. All history was a palimpsest, scraped clean and reinscribed exactly as often as was necessary."

This quote tells of how the party changed any document that they wanted to make anything they wanted true, for every written document would be changed to make it true. Thus, in doing this, no one had any evidence otherwise, therefore, what they changed actually became history.