Are you referring to anachronistic documents that werent produced at the time they claim to be from, or if the clerk was lying at the time like CIA fake passports for agents?
Scientists can date objects with atomic analysis (radiocarbon dating for example), compare it to other better authenticated objects from that time and see if production techniques and materials match.
If you try to see if it was false at the time, you would have to find other evidence of facts and try to put a bigger picture together, like any detective.