AAA rates for the following year get released in July/August each year. So if you are calling in June 2006 for January 2007, the rates will not have been "released" yet.
I usually make my room-only reservation and then start to call in July to inquire about AAA rates. Once they are available, I have them applied to my reservation.
The room-only rates can only be applied for a (I believe) 13 night period (used to be 10), so sometimes you are required to hold two separate reservations - checking out and checking back in. Not guaranteed, but in most cases you will have the same spot and will not be required to move.
Other posters are correct, in that only a certain amount are available - once their gone, they are gone - unless someone cancels.