We have a debit card transaction attempting to post this morning from a card that has been closed for over a year. The customer had his card/checks stolen at that time, and is disputing this charge, too.

How does something take a year to come through on a debit card authorization? Isn't there some sort of timeframe allowance for this?

The Acquirer is to blame. You should check your chargeback rights for Late Presentment.

def late presentment chargeback.

There is a chargeback right for transactions where the authorization is over 180 days old. Authorizations only use a DDD format not YDDD so that is why Visa processed a transaction that is so late.