Given the fact it is impossible to reconcile some overpunches, even the seemingly impossible/improbable cannot be ruled out. If the wrong punch was used, you could get any possible combination in any year as any punch (including letters) could be used. Most of the time the correct character punch would inevitably be used, but this can't be guaranteed. e.g. a 9 instead of an 8 is only a case of picking a punch from the adjacent bin, or choosing one that was replaced in the wrong bin. All options must be on the table.