Did you actually try to select one of the January dates?
We are there from 12/30 until 1/3 and whilst it shows the January dates on the first two screens, when it gets to the actual booking screen it says nothing is available
I have been trying since the day the December dates have been released, and could still get NYE or 12/30 reservations, so I'm pretty sure that it isn't just already fully booked, but rather that jan dates haven't yet opened up