It's always easiest if you chart out what you are doing.
Taking the March Use Year.
Points received March 2005 can be used for trips through the last day of February.
Points received March 2006 can be used for trips from March 1, 2006-Feb. 28(?), 2007
You are taking a trip in December 2005 and needed additional points. You "borrowed" from the March 2006 allotment.
The March 2005 points used for the reservation must be used for the trip or will expire Feb. 28, 2006 -- unless you cancel 31 days or more before arrival and are within your banking deadlines. Then you will have the option of banking. If you cancel the December reservation 31 days or more from your arrival, you can still bank the points subject to your banking deadlines (100% August 31, 50% November 30, 25% December 31)
The March 2006 points you borrowed and used for the reservation are locked. If you cancel, they must be used no later than February 28, 2006.
If MS says something that you don't understand, don't be embarassed to say so. If it's a problem understanding the person you have on the line, you can hang up and call back and ask for a supervisor to explain it to you. It's important not to say yes to something you don't understand. You could be making a mistake with your points.