Historically, Marriott has allowed you to extend ONE certificate to complete a booking after expiration.

FYI These are the only certificates in the system that are initially good for 13 months. Your new certs will post exactly one month before your current ones expire.

Also, don’t bother calling anywhere other than the designated phone number for the club level upgrade certificates. I’ve found the agents that answer this line are the only ones trained in how to apply the certs and the rules surrounding them - including making sure you get the $100 credit for a 2-night stay in conjunction with the upgrade, if it is available (sometimes it is and sometimes it isn’t, but on their end it shows up as two separate booking categories - if an agent clicks the wrong one, you won’t get the credit).

Everyone else I’ve ever talked to, including my Ambassador - is clueless about how these certs work.