I actually spoke to a young lady who said she called every day for three months to get the Cinderella Breakfast to no avail. She walked up and was seated in about half an hour. I suspect that they only set aside a certain percentage (85%?) for ADR's. On the flip side, with our hard fought adr's, we were seated in no more than 10 minutes each time.
I few years back a large group of Disney fans (20ish) were going there for dinner. We were left out of the reservation because there was not enough space, even though eating at the same table was not a requirement (or even possible). Anyway, we (two) decided to show up at the reservation time. We got a table and we were seated before the others. I think they were broken into something like 6,4,4,4,2 - plus us at our table for two.