Room Categories are the biggest thing that can change from day to day with these discounts. For example, I had to book a water view room the one year because standard wasn't available. I kept checking back and finally a couple weeks later a standard room opened up.
You also may find that the availability you see today on the Disney Website may vary greatly from the rooms and categories available on the discount. There's always speculation on whether Disney sets aside rooms for these discounts or not, but there is no conclusive answer to that.
My best advise is to be flexible. You may need to move up a room category (which would erode some of your savings) to take advantage of the deal. Also keep checking back in the event your desired room type (or a more optimal option) opens up!