backdate

/ˌbækˈdeɪt/ /ˈ--/ verb [T]

Definition

› to make something effective from a date earlier than the present date: They agreed that the pay increase would be backdated to July. Those signing up before October will have their pension payments backdated.

› to put a date on a document that is earlier than the date when you wrote it: The jury's verdict recognized that backdating options with intent to deceive is a crime. backdate a cheque → Compare post-date

(Definition of backdate verb from the Cambridge Business English Dictionary © Cambridge University Press)