Correct, Saratoga Springs contracts are through 2054 while all other DVC properties go until 2042.
One thing to keep in mind when buying resale is how many points are currently available on the contract. What I mean is that the seller may have used up all of this years points and possibly even borrowed (and used) all of next years points. So you might buy it now but not be able to take a trip until 2006. Other contracts may have a bunch banked meaning you could take a bunch of trips immediately. Lots of little things to think about but if you have a good resale agent, they should be able to help sort throught it all. I've heard good things about the Timeshare Store.