Maybe Jim or Brian can speak to Wyndham which I believe has very limited priorities for some situations.
Wyndham has a couple of different products, depending on where (and in some cases when) you purchase. Some have a specific underlying fixed week, and you have advanced rights only to that specific week. More recently are "undivided interest" (UDI) deeds. Those deeds have advanced rights to the home resort, at any week. Finally, the newest product is "club Wyndham access" (CWA). This is a trust that blends inventory from all owners together, and owners have advanced rights to any of that inventory, without a notion of "home resort".
In Wyndham's system, advanced rights are not particularly important with a very few exceptions: lower-point-value resorts in Myrtle Beach and Destin in summer, event weeks in New Orleans, Cherry Blossom festival and July 4th in DC, etc. That's partly because the system is just so much larger, and it's also partly because Wyndham's system has longer booking windows: 13 months for "advanced" and 10 months for "regular" bookings.
DVC has a consistent 95% to 100% occupancy rate. Two years ago they said that it was between 85% and 100%.
A timeshare system is designed for full occupancy, year round. For every night's worth of points it takes to book something, someone owns those points. There are only two ways for occupancy to be anything less than "full" on any given night. One: some Member allows their points to expire unused. Two: some Member has performed an internal exchange to
DCL, the Disney Collection, or ABD, and CRO was unable to rent the room backed by the relinquished points. Two years ago we were in the midst of the recession---significantly worse than we are now. It would not surprise me to hear that Members were allowing points to expire more frequently in 2009 than 2011, because after all the room is only one part of the vacation costs. Likewise, it's not surprising that CRO found it more difficult to rent rooms in 2009 than in 2011.
It is true that point reallocations are intended to smooth out mis-matches between demand and supply, but if Members are using their points, the rooms should always be full no matter what.