First weekend in Dec is an Orlando Informer Meetup weekend - I suspect that has a lot of hotels booked for that Fri night (and Sat).
But other than weekends being harder to get / limited availability, it is really variable and changes a lot. Might be an AP rate on Mon-Wed but Tues- Wed has nothing (why?). Then a week later there is availability for both. Then a week later there is no regular room but club level shows up. Then a week later all rooms are available. Book what you like, then keep checking for your perfect combo since you just never know.
Took weeks to get a single Thurs night at Portofino club in Oct (I only wanted the Thurs); in the meantime a club room was available at all the other hotels or for all the surrounding weekdays at Portofino.
When you change your booking, your deposit is transferred as long as it's the same hotel. If it's the exact same room but a better price, you can add/drop a child to let you change the booking, or else you have to cancel & rebook, which takes a few weeks for the original deposit to be refunded.