When I originally renewed my subscription with TGM, our next trip wasn't planned until 2010, but the latest option was 2009. I renewed anyway and sent an e-mail explaining the situation. Mike replied that it was fine, to just change my date when it got closer to the vacation.
Now I've turned my husband into a mini-disney addict and we've had one trip since plus another 2 booked BEFORE the 2010 trip!