Previous posters are correct. Unlike regular hotels, DVC resorts cannot be knowingly "overbooked". Hotels know that there will be a certain percentage of cancellations and if not they just assign an upgraded open room to a guest. But DVC is not allowed to do this...that's why the cancellation penalties and restrictions are pretty severe.
So the only time an upgrade should happen is if some rooms are out of commission that they didn't expect. Maybe a maintenance issue cropped up in a villa that wasn't scheduled to be out of commission.