Carter gave preemptive pardons to all the Vietnam era draft resisters, whether or not their crimes had yet been recognized. Which mean Clinton was pardoned. Andrew Johnson issued fairly broad pardons after Civil War IIRC.
Is it possible “some” draft resisters were already charged, and therefore the nature of crime was in place already.
As for the Biden family, the optics would look terrible if president JB issues full pardons to all Biden’s before anyone being charged. It would have the aura of pervading guilt.