The answer is definitely yes. Easiest way to see this is to make yourself a use year calendar. This one would be for an August use year.
<b>use year.....vacation dates</b>
2004.....Aug 1, 2004 through July 31, 2005
2005.....Aug 1, 2005 through July 31, 2006
2006.....Aug 1, 2006 through July 31, 2007
2007.....Aug 1, 2007 through July 31, 2008
2008.....Aug 1, 2008 through July 31, 2009
2009.....Aug 1, 2009 through July 31, 2010
Your september vacation will be within your 2004 use year, so you will need to use 2004 year points.
Your regular 2004 allotment will be good for your 2004 use year. You can borrow your 2005 use year points and put them into your 2004 use year. Thus they also would be good for the 8-1-04 through 7-31-05 timeframe.
Note: MS will only borrow the number of points necessary to complete the reservation. You don't borrow the entire amount of points. If your reservation required 250 points, you would use all 150 of your 2004 points, borrow 100 of your 2005 points, leaving 50 2005 year points still available.
Remember, once borrowed, points cannot be returned to their former use year.
You make your reservations 11 months/7-months from your vacation check-OUT date. Making reservations has nothing to do with when you get your points. It is only important that the points are going to be there at the time the vacation is taken. So even though you haven't received any points yet at all, MS will still make the reservation using the points that will be in your 2004 use year by the time of the actual vacation.
Hope this helps