If you book a December 2015 trip it's in your 2015 UY. Depending on what points you use will determine what happens along with when you cancel. If you cancel more than 31 days out, points are returned to your account with the same status. So, banked 2014 points would still be banked, 2015 UY points would still be current and would be eligible or banking, and any borrowed 2016 points would still be borrowed and locked into your 2015 UY