it doesn't matter where you are in your UY when you call to book. booking windows are based on where you own...nothing to do with UY.
so you always need to start by figuring out during what UY your stay takes place.
if you want to book aug 1, 2013 for 5 nights, that takes place during your 2013 UY. so when you book that stay you can use current 2013 pts (current based on the dates of the stay) + banked 2012 pts (if you have any left) + borrowed 2014 pts (if you need them).
for booking your home resort, you can call 11 months ahead. so you could call on sept 1, 2012 to book aug 1, 2013. when you make that call, you can borrow from your 2014 UY if needed.
if you want to book july 1, 2013 for 5 nights, that takes place during your 2012 UY. so when you book that stay you can use current 2012 pts (current based on the dates of the stay) + banked 2011 pts (if you have any left) + borrowed 2013 pts (if you need them).
for booking your home resort, you can call 11 months ahead. so you could have called on aug 1, 2012 to book july 1, 2013. when you make that call, you can borrow from your 2013 UY if needed.
the big issue with a july stay (any stay at the end of your UY) is that your banking window closes march 31...so if you cancel a july stay in april, your pts are still all stuck in that use year and cannot be banked forward - they will expire on that july 31. if you have an august stay and cancel over a month in advance, you have until the NEXT march 31 to decide to bank any current pts and until the NEXT july to figure out how to use any banked/borrowed pts before they expire.
please bookmark this thread for reference as it is the detailed UY guide for dummies and otherwise
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http://www.disboards.com/showthread.php?t=1942668