Use Year is the month each year when you points will be renewed.
If you ourchase now with an October UY, you will get all points from 2005 and wil lhave another allotment available on October 1, 2006. UY also determines your banking deadlines (6 months to bank 100% of your points, 9 months to bank up to 50% and 10 months to bank up to 25%), but it has nothing to do with when you may make a reservation.
Basically, any points banked into the next UY ,will expire at the end of that UY. Points may also be borrowed into a UY and must then be used during that UY since they can not be banked.
If you purchase now- the 2005 points must be used by September 30, 2006 or banked at time of purchase to be used in the next UY (they would then expire on September 30, 2007). The points available on October 1, 2006 will expire on September 30, 2007 unless banked into the following UY to gain an additional year to use them.
If you will not need your 2005 points for a trip prior to 9/30/06, be sure to bank them for use next UY.