While I don't know the formula used, DVD doesn't have to hold back anything for possible future reservations. Their obligation is to offer point reservations for the same percentage as has been sold.
Traditionally,
DVC has declared more into inventory that has actually been sold, so they do already anticipate the needs for the sales. In that scenario, they can propbably track the inventory already booked beyond the actual sales % and balance that against the point needs of the future.
In addition, 60 days prior, all unreserved member inventory is released to CRO for cash reservations anyway.
If there are available rooms as sales increase, those rooms would be made available for point reservation, but it would be unreasonable to expect the developer to hold back more rooms than necessary when they can recoup expenses by renting those rooms.
I'm sure DVD has some formula they use to keep the inventory as fair as possible, but don't assume that they are holding back any rooms just in case the sales % increases. Until someone buys those contracts, DVC still owns the property and, by contract, can rent their inventory as desired.