It's all pretty messed at the minute. And the whole 'guaranteed between 30th November and 15th December' business has fucked shit up even more. If it was true, starting tomorrow there would be a constant back-order on all units until every last order was fulfilled. Somehow I doubt that'll happen.
Anyway, like I posted before: It seems that(probably) because the initial preorder allocation of ZombieU bundles was so small, a lot of extra unreserved units have come into stock (since yesterday).
You'd be better off just taking a trip to HMV tomorrow morning and buying one in person:
http://hmv.com/hmvweb/displayProductDetails.do?ctx=280;0;-1;-1;-1&sku=967881