Understanding Use Year -
Use year is the month your points are renewed each year. You have one year to use the points before they expire (unless you bank them).
Use year determines your banking deadlines, but it has nothing to do with when you can make a reservation. You can always call 11 months prior to check out for a reservation at your home resort and 7 months prior to check out if you want to reserve something at a non-home resort.
For example, let's say you get April for your use year. Let's say you decide to buy 200 points.
On April 1, 2007 you received 200 points to use for stays between 4/1/2007 and 3/31/2008. Those would be considered your current use year points for the 2007 use year and any stays that occur during that time period.
Your 2007 use year points are good for stays between 4/1/2007 and 3/31/2008.
Your 2008 use year points are good for stays between 4/1/2008 and 3/31/2009.
Your 2009 use year points are good for stays between 4/1/2009 and 3/31/2010.
etc.
You may bank points one use year ahead and borrow from one use year ahead. Beginning in 2008, you have 8 months to bank up to 100% of your annual allotment of points. For an April use year, that means you need to call to bank before the end of the following November.
Let's say you want to stay in May of 2008 and your stay will cost 500 points. Let's assume you banked your 2007 use year points. So now they are good for stays between 4/1/2008 and 3/31/2009.
May, 2008 falls within your 2008 use year. For that reservation, you may use current use year points from the 2008 use year, any banked points (originally from your 2007 use year) and/or you may borrow points from your 2009 use year.
Banking and borrowing are final transactions. If you cancel a reservation made with banked or borrowed points, they cannot be returned to their original use year. So they would expire at the end of the current use year unless they were used before then. You may not bank or borrow the same points more than once.
Let's say you have to cancel that May, 2008 vacation. You call to cancel it in March, 2008 (which is more than 31 days prior to arrival). To make that reservation, you used 200 current use year points, 200 banked points (from 2007) and borrowed 100 points from 2009.
After you cancel, you would have 300 points to use or lose before the end of the 2008 use year, which is 3/31/2009. The 200 that were banked and the 100 that were borrowed can't be "unbanked" or "unborrowed". But you could bank the 200 points that are from your 2008 use year if you don't need them before 3/31/2009 as long as you call to do it before the end of November, 2008. Then they would be good for stays in your 2009 use year (4/1/2009 - 3/31/2010).
ADVICE: If you travel about the same time of the year on a regular basis, it's best to choose a use year that falls no more than 4 or 5 months prior to that time.
Use year only matters if you have to cancel a vacation that was scheduled to occur late in your use year. That's because banking is limited late in the use year and you wouldn't have much time to reschedule before the points expire.
For example, let's say you take the same 500 point vacation but schedule it for January 2009. January 2009 falls within your 2008 use year and you use 200 banked points (from 2007), 200 current use year points (from 2008) and borrow 100 from your 2009 use year. Let's say you find out in early December 2008 that you have to cancel the vacation. Since your banking deadline (11/30/2008) has passed for the 2008 use year points, you now have to use 500 points before 3/31/2009 or they expire. If you normally travel in January, February or March, April would not be a good use year for you.
Many owners never have to cancel a vacation (lucky them, LOL) so they don't worry about use year. Remember, use year has nothing to do with when you may call to make a reservation.
Keep in mind that your travel pattern may change over the course of your ownership. What starts out as a "perfect" use year may end up to be not so perfect.
Hope all that helps you understand how use year works.