dec 2011 pts are valid for stays from dec 1, 2011 to nov 30, 2012.
dec 2011 pts can be borrowed into 2010 - making them valid for stays from dec 1, 2010 through nov 30, 2011.
you could have called to book a stay at your home resort for dec 1, 2010 starting as early as jan 2, 2010 (the first day in jan that MS was open, IIRC).
so you could have called as early as jan 2, 2010 to borrow your 2011 pts to book a stay starting dec 1, 2010.
edited to add: remember that UY month generally has nothing to do with when you can call to book - that is based on your home resort.