You may always book at Home Resort as early as 11 mos out if you have points that will be valid for use during the dates of the trip. These may be Banked, Borrowed or Current(UY during which trip takes place) allotments of points or combination.
On Dec xx 2009 at 11 mos window MS could have reserved Thanksgiving 2010 trip utilizing :
banked Aug 2009 & Oct 2009 UY pts and/or
current Aug 2010 UY & Oct 2010 UY points &/or
borrowed Aug 2011 & Oct 2011 UYpoints.
But, if I remember correctly, you couldn't use points from both Aug & Oct contracts to book a single night; if you needed to do this then it would be as poster
Toddylu said about needing to do a transfer because 2 different UYs means 2 separate contracts:
ie your 100 pt Oct contract can book you 3 nights at 27 points per night but for night 4 you only have 19 points left in this contract
so you'd need to transfer 8 points over from Sept contract to Oct contract to book that night.
Best wishes on your planning, HHI is a great resort
