optimisticAs long as the core nights are still available, I expect that you will be able to get the shoulder nights. Once the core nights are gone, I expect that will be it; however, until that happens, don't let the lack of shoulder nights discourage you from making your booking and asking for the full range of nights.
(I am not speaking from insider information here. This is what is on the Sasquan web site and what has been posted in public elsewhere. I'm on the Sasquan committee as an area head, but my job isn't in the hotel/facilities division.)