I just called in to Marriott customer service. I have 4 expiring on 6/30 and 2 in early October. They claimed that ever since covid, they've been extending certificate expiration dates automatically. Alas, no more. They stated they aren't even going back to the old pre-covid days where you can call in and request extensions. Not only do you have to book by, but you need to stay, and actually leave the property by the expiration date. Looks like this is the end of the road for being able to hoard certs.