The resort has 2,112 rooms.
The current ADA requirements apply to hotels designed and constructed after January 26, 1993. Since CBR was constructed in about 1988 or 1989, those guidelines would not have been required at that time. They did renovate a few years ago and would have probably come up to the requirement at that time.
The current requirements for the number of accessible rooms, call for a hotel with 1001 rooms and over to have 20 handicapped rooms plus 1 for each 100 over 1000 (plus 1 room with a roll-in shower for each 100 rooms).
I'm not sure if the 21 rooms you mention are the roll in shower rooms, but that may be what it is because that does meet the 1 room with a roll in shower for each 100 rooms.
(The 'handicapped' rooms in the requirement are ones with grab bars, raised seat toilets, but not roll in showers).
From what I have read/heard over the years, it sounds like the handicapped accessible and roll in shower rooms are distributed around the resort. You are right that they would all be on first floor because there are no elevators.
If you want a room in a specific area, you can make the request at the time of your reservation. From what I have read, just needing a handicapped room may not get you a 'preferred' location. So if you want one in that area, be sure to ask if there will be a higher fee (as there is for that location for people who don't need accessible rooms).