I assume you are talking about banking 2003 use year points. With a December use year, the deadline to bank 100% of your points is May 31.
If you are buying directly from Disney, there will not be any problem at all. I'm sure your deal will close long before the end of this coming May.
If you are buying a resale, it is possible that the contract will not close in time, but the odds are very much in your favor. If you have any doubts at all, ask the seller to bank the points for you.
HTH.