Our contracts allow any rooms not booked by owners 60 days out to be rented for cash. It is called breakage inventory and we get some of that as a credit in our dues. Every resort hits the maximum amount...2.5%. Any additional money goes to DVC and IIRC, to BVTC as well.
DVC has the ability to anticipate what rooms might still be there and pull them early based on that as well. They obviously don't pull all inventory or we would never see any rooms, and holding points are restricted to bookings 60 days or less so that is another reason you see things still there. But, DVC is the one who decides what is or is not taken. We all agree to this aspect as part of the contract.
We have heard that sometimes, they can "pull back" a room that is sitting there for cash, if it was indeed part of breakage income (not if it is a trade or was booked using DVD points).
When DVD offers new buyers a welcome home visit, it is either from rooms they booked using their own points, or in the case of resorts that are in active sales, like RIV, they use rooms not yet declared into the condo association for owners to book. Until those rooms are declared, they belong to DVD to sell for cash. It is why they are able to get new owners rooms when it doesn't show on the website...because they belong to DVD still. RIV is about 50% declared, which means on any given day, only 50% of the rooms can be booked using owner's points.
What most likely happened in your case, is that DVD is letting you have one of their rooms to make this shift happen...if it was normal inventory available to owners, it would have been on the website.