Im sure its happened before at some point but ive never been that lucky. Last minute cancellations aren’t super common. You can be put on the waitlist for a concierge room if there’s none available when you book or you decide at a later date you want to upgrade prior to embarkation day. But when a concierge room becomes available they send out an email to everyone on the waitlist and it’s first come first served. Never been successful doing that either.