Spiceycat:
Had you already done any banking? In Jan/Feb, you are still in your 50% window, so if you hadn't banked anything yet, the add-on would probably be bankable as it would be less than 50% of your new total of points. (ie, if you had 200 points and added 100, you could bank the 100 because it would only be 33% of your 300 point total.)
I added on in January (also with a June use year), but was not allowed to bank the add-on because I was already at over 50% banked. They would not make an exception.