I'm making up numbers here, but if 20% of a property has been declared into inventory, I don't think that they can sell the theoretical max of 30% of a room/view type for one FW. If they did, all other owners would be blocked from booking that room/view during that FW until more inventory is declared. Perhaps CFW is a good example? But as you said, yes, FW sales are at
DVC's discretion.
And because intamin was asking about FW48/49/50 possibilities, just a couple of cautions:
FW50 could begin as early as Dec 9 check-in, but could begin as late as Dec 16 check-in / Dec 23 check-out (2029, 2035, 2046). If you're on a DVC Sorcerer AP, you'll hit some blockout dates some years.
FW48 frequently begins the Sunday after Thanksgiving which is a very busy travel day. If flying, expect airfare to be a little more expensive and airports to be crowded.
I understand wanting to buy soon so you don't lose a year's worth of points. Have you decided on PIT? I don't know what the current FW48/49/50 status is at RIV if that's an option you'd consider.