There are a number of factors that affect the amount of points DVD has available to sell for VGF and the other 'sold out' resorts. As I mentioned before, there are always some sales in the pipeline that have not closed. Usually, DVC sales close in 2-3 weeks, but there are times when a buyer sits on a deed for months before they return the paperwork. Three or four month delays are not that unusual and occasionally there will be a buyer that doesn't return the paperwork for six months . There are probably a few customers who never return the paperwork but I don't know how long DVD waits until it finally gives up on them. Until DVD decides to cancel the pending transaction, those points can't be sold to another customer.
Another factor involves the number of points reacquired by DVD. In June 2015, DVD reacquired 1,500 points: 520 points via foreclosure and 980 points via buybacks. Through July 27, 2015, DVD has only reacquired 210 points. The more points DVD reacquires, the more points it has available . . . but not necessarily right away. The deeds reacquired by DVD could be stripped of some or all of their current year's points. The 210-point deed reacquired by DVD in July had an August Use Year, but I don't know how many, if any, points it had left for 2014 or 2015. If it was completely stripped with no points available until August 1, 2016, then DVD won't sell those points until August 2016 at the earliest.
Yet another factor affecting DVD's available point inventory depends on how DVD is using its own points. As most of you know, DVD is required to retain at least 2% of a resort's total points for itself. It can keep more than 2% (which is often the case), but is prohibited from keeping less. DVD can use the points it owns in different ways. It can use them for cash reservations, it can use them for marketing, or even let them sit idle and unused. For example, DVD could have used 148 of its own VGF points to fund a 7-night Lake View Studio cash reservation for this September. If the cash guest were to cancel the reservation today, then DVD would suddenly have an extra 148 points freed up that it could sell as part of a DVC deed (assuming DVD did not need to retain those points to satisfy its 2% holding at VGF).
As you see, DVD's inventory of points available to sell to the general public can be very fluid and changing from day-to-day. It does not surprise me if there are no points available one day, then hundreds available the next day, and then no points available the day after that.