We had one of the aft handicapped Cat 3's booked for this November.
About 4 months before departure, we got offered a Cat 2. which we greatfully accepted.
About six weeks after that, we got another call, offering the Roy - Ka-Ching!.
It does happen, but I am guessing our occurance is pretty rare.....
8534 is a pretty great room, so you are doing ok, but we understand how cool it is to get one of the others.....
Good Luck!