If you are making a reservation for Dec 2013, then you have to use points in your Dec 2013 UY, which starts 12/1/2013. Your Dec 2012 points are only good for stays through Nov 30 2013. If you bank you Dec 2012 UY points prior to 7/31/2013, then they will be available for use to make a reservation in the Dec 2013 UY.
When you do finally bank those 2012 points, MS probably would be able to re-allocate those points to your Dec 2013 reservation and release the 2013 points that were used so they can be used later in the 2013 UY. When I bought a resale last year, they were able to do that with some of my new points that were banked points and had to be used in that UY.
Is there a reason why you don't want to just bank those 144 points now? If you have no plans to use them, that would probably make things easier.