I have a listing that just went under contract. The sellers already had a home warranty on the home when I listed it. Their policy is paid up through their anniversary date which is May, 2010. The buyers will get this warranty (we are clsioing in Oct), but it will only be valid thru May, after which they can purchase the warranty for another year. Perhaps this is the case with your home. We told the buyers about the partial year coverage in advance.
Is the warranty with American Home Shield? If it is, and the sellers took it out when they first listed the home, it shoud transfer to you for a year following the closing. If it was already in place, then it might be a similar situation as my client's home.
Hope this helps.
Prudential NJ Properties
Almost all home warranty companies that I have dealt with do cover a full year. You should have received a copy of the policy/brochure explaining the coverage. It is also possible that the seller had coverage beginning from the listing date. If the listing date was in 12/08, then perhaps that is why you are seeing a date of 12/09. The best person to investigate is either your agent or the seller's agent. Good luck!