We just did an add-on for VWL 150 points, Sept use year. Our guide said there was 1000 points for September, thus I would assume there are a bunch of total points. When you do an add-on, you have to have your current use year, so that might be a limitation.
With our add-on, we did get MB. Better yet, they gave us 2002 points, thus we used them for MB and have all of our 2003 points. This deal makes it almost as cheap as a resale, but with the speed of Disney.