First, there is no Jan UY (I know it was just your example) so let's go with Feb UY instead.
If you have a Feb UY, that is when your points become current every year. So, every Feb 1st, you have 100 points that are now available for use from that day until January 31st of the following year.
The only way not to have points on that first day is if they have been borrowed into the previous UY.
You will always have the first 8 months of the UY to bank your points. For Feb, that gives you until July 31stFeb UY need to be banked by September 30th not July 31st of every year to bank them into the next year. So, 2010 points can be banked by July 31st in the 2011 UY. Once banked, they will be goo from Feb 1st, 2011 through January 31st, 2012.
If you travel on banked points and then cancel (at least 31 days out--different things happen if you cancel with less than that), those banked points will expire at the end of the UY they are in. So, if you had a reservation booked for December 2010 (your Feb 2010 UY) using banked points from 2009, and cancel that trip, those 2009 banked points would expire on January 31st, 2011.
What is most important, IMO, about UY is that you want one that allows you to travel near the beginning of it so that you have a lot of flexibility in using your points up if you have to cancel a trip, change a trip, or have to borrow points for a trip.
When you travel outside the banking window near the end of the UY, and cancel, you don't have a lot of time to re-book a trip to use the points.