We bought at SSR and at AKV because those are our favorite resorts and we'll never be unhappy staying at either. Now that said, I've made a variety of reservations at other resorts with our points. This past January, I made reservations for BWV in a Standard View Studio 7 months out, and then when I had points in holding due to a problem with our October trip I was able to upgrade the BWV to a Preferred View with those points, though I did have to waitlist for the upgrade.
In 2006 sent some friends down to VWL for Spring Break. They told us where they wanted to stay 5 months out. Originally was only able to get SSR, but waitlisted and 2 months out VWL came through for the whole week.
This past Saturday, DH and I decided we wanted to spend our anniversary at AKV, 8 nights in late October. When I called I was able to secure all 8 nights in a Savannah view studio at 7 months and 2 weeks from trip. Now would I have gotten all 8 nights if I'd waited another 2 weeks, probably not, but if you are flexible in room type then your home resort should be fairly easy to secure any time in the 4 month window.