The scenario crisi described happened to us (with an eventually happy ending). I was in close contact with our guide about VWL selling out (and it was publicized all over the boards). We had to wait to see if we were going to have a big expense or we could use that $$ for a small add on. About every 3 weeks, our guide would say, "I think you'll be OK for another xxxxx amount of time", but he never guaranteed anything. We had all sorts of official notice that the resort was 'selling out'.
We absolutely DID NOT understand that we had to purchase the same use year --- don't know why it never came up in conversation and we didn't recall reading that, probably because we'd only been members about 7 months and just didn't pay attention. When I called to purchase the add-on, I was totally shocked to find out our use-year had sold out. We still have no idea what suddenly happened. Another guide suggested that they never know when someone will purchase hundreds of points. It was very, very disappointing, to say the least, but we just couldn't have made the committment to purchasing 60 more points when we thought we might have to spend $$$ for a medical reason.
We immediately went on a wait list and I'd check in every couple months with our guide. We got the add-on within 6 months and have been trying to figure out why we STILL don't have enough points.