I often suggest people make a chart for their specific use year. A May use year would look like this:
<b>Use Year.....Vacation Dates</b>
2004.....May 1, 2004 through Apr 30, 2005
2005.....May 1, 2005 through Apr 30, 2006
2006.....May 1, 2006 through Apr 30, 2007
2007.....May 1, 2007 through Apr 30, 2008
2008.....May 1, 2008 through Apr 30, 2009
2009.....May 1, 2009 through Apr 30, 2010
and so on.
Use year indicates when those point may be used for vacations. If you bank 2004 points into 2005, then those points can only be used for a vacation that occurs within your 2005 use year: May 1, 2005 through Apr 30, 2006.
2004 points banked into 2005 would expire on Apr 30, 2006.
If you wanted to have a vacation in December 2005 (which is in your 2005 use year), you could bank your 2004 points into 2005, and additionally use any 2005 regular points if you wanted, and also additionally you could borrow 2006 points into 2005. Uning this method you could have a vacation in Dec 2005 that required up to 3x your regular allotment of points, via banking and borrowing.
Keep in mind that once points are banked they cannot be returned to their original use year, nor can they be banked again into the next following year. Thus if you bank UY May 2004 points into 2005, those banked points can ONLY be used for a vacation between May 1, 2005 and Apr 30, 2006. You cannot return those points to 2004 nor may you bank those same points into 2006. You could however bank your regular 2005 allotment of points into 2006 if desired.
Hope this helps