In this answer to a question regarding stolen/cancelled cheques, it is stated:
A little known fact about stopped checks is that the stop is often only good for a short period of time (only six months at some banks) at which time the 'stops' are no longer valid. This means you that you'll have to reissue the stop payment order for the remaining checks.
Why is this? If a cheque has a stop-payment order put on it as a result of said cheque being stolen, it is unlikely bordering on impossible that the cheque will ever be recovered, leaving no good reason for it to be made payable again; why not permanently void the stolen cheque?