Updating "Call me crazy, but . . ." Thought

Why is that you can update but not downdate?  Why can't you nowdate? Or latedate? Or belateddate?  Up and down and front and back go together, but not in the case of updating.  You can, of course, go up a hill and back down it, or go back and forth, but in those cases you are always going and returning to the same two  places.  Backdating is not apposite updating the way back and forth are but the opposite of updating:  to backdate is to lie, falsify, to forge a date that didn't exist.  To update, by contrast, is to revise and give the most correct, accurate account.  But is updating really totally opposed to forgery?   If you are always saving by erasing earlier versions (like Freud's mystic writing pad), is the saved version not also a forgery of sorts, a cover up?