your UY month has nothing to do with when you can call to book. zero.
you can call in jan 2012 to book dec 2012 because you can book your home resort 11 months out. for a stay in your 2012 use year, you can use banked 2011 pts (if any), current 2012 pts (doesn't matter if your 2012 UY has started yet when you call to book, they are "current" based on the dates of your stay) and borrowed 2013 pts.
doesn't matter if your UY started in june or december, you could still call in january and use pts from any or all of those use years.
so go ahead and call in jan 2012 and borrow the pts from 2013 if you need them to complete the reservation.