Yes, you understand correctly. October 2007 is 11 months prior to a September 2008 vacation. September 2008 falls within your 2008 use year (4/1/2008 through 3/31/2009).
For vacations that fall within your 2008 use year, you could use:
* Banked points from your 2007 use year (if you banked any),
* Points from your 2008 use year (which would be considered current use year points for reservations within that time frame) and
* Points borrowed from your 2009 use year.
Assume you know that if you cancel the 9/08 reservation, the borrowed points would remain in your 2008 use year. You cannot return them to the 2009 use year. If the borrowed points are not used prior to 3/31/2009, they would expire and be lost to you.