When the same thing happened to me I just contacted apple (through iTunes support iirc) and after a couple of days they came back to me with instructions on how to get the January update again for free. Basically they look at your iTunes purchase history and set the update has having not been downloaded when you do a check for purchases in iTunes it downloads on its own.
Like I said though it took a few days - not sure how quick they'll be given the number of calls they'll get this week!