Make yourself a chart for your use year. For a March UY, it looks like this:
<b>Use Year......Vacation Dates</b>
2003......Mar 1, 2003 through Feb 29, 2004
2004......Mar 1, 2004 through Feb 28, 2005
2005......Mar 1, 2005 through Feb 28, 2006
2006......Mar 1, 2006 through Feb 28, 2007
2007......Mar 1, 2007 through Feb 29, 2008
For you, a vacation in Dec 2004 requires points from your 2004 use year. You will receive those points on Mar 1, 2004. You make the reservation based on your 11-month/7-month windows, not on your use year. When you make your reservation in January they will use your 2004 points for a Dec 2004 trip. You are not borrowing points.
Now, suppose you own 150 points and your vacation in Dec will require 200 points. In that case in January when you make your Dec 2004 reservation you would use all 150 of your 2004 points (that you get Mar 1, 2004) and you would borrow 50 of your 2005 points (that you would normally get Mar 1, 2005) to make your 200 point reservation.
Always remember the points used for a vacation use the vacation dates themselves to determine what use year the points must come from. You can bank points from one use year to another, or borrow from one to a prior year. When you do so, those banked or borrowed points become part of the use year they are moved into.
Making reservations is based strictly on 11-months/7-months or less from your vacation check-out date.
Hope this helps.