I wish there was something I could do for you
It doesn't really have anything to do with being pre-paid, it's all de pendent on what people drop between now and when you're looking for and that's just such a coveted restaurant! But as you see openings DO pop up; do you have a search set up with TP or Mouse Dining or an agent looking for you?
People cancel "last minute" and it's often within a week to a day or two of their reservation. Right now there are also folks who are still on the fence for their Nov./Dec. trips and have dining but may end up not going at all. I know it's a pain but keep looking and good luck!