antedate
verb [ T ]
uk/ˌæntiˈdeɪt/ us/ˈæntiˌdeɪt/ US
to put a date on a document that is earlier than the date it is signed:
an antedated check
Compare
backdate
post-date
to have existed or happened before something else:
antedate sth by 6 months/ten years, etc. Adverse information that antedates a consumer report by more than seven years is not reportable.