Boeings updates their order book on a weekly basis, perhaps there were 6 deliveries in the last week of December?
Might be. I was on the BO web and there were the deliveries not yet, but the orders were complete up DEC 31. So the unfulfilled numbers are up to before publishing the DEC numbers.
Anyway there was really 6 77W deliveries in DEC i.e. the explanation is there - no mess. Also the 6 Chinese orders are not yet in the numbers downloaded by XWB - so funny as it is those 224 777-classics are valid as of now.