Two different delivery processes for aircraft to military customers. DD-250 is the ownership delivery of the aircraft. Once the DD-250 is signed, the military actually has legal ownership of the aircraft. At this point, the aircraft is on the books as military owned and delivered. The second delivery is actually moving the aircraft from the factory to the receiving station, and the military actually taking physical custody of the aircraft. There is a time lag between DD-250 and physical delivery, that can be as short as a couple of weeks and as long as several months, depending on a large number of factors.
In the case of this particular aircraft, I would suspect that it was DD-250'd prior to 1 Dec42 and not ferried out until after 1 Jan43. The natural finish directive probably also had a serial number break in, so that anything on the line already painted, would continue and not be sent for stripping prior to delivery.
Working for a manufacturer, I've seen aircraft DD-250'd and not leave the production facility for months or even years. What happens with these aircraft is that they are "bailed" back to the manufacturer for either testing purposes, or modification development. The military retains ownership, but in effect loans the aircraft back to the manufacturer for the designated purpose and for a specific period of time.
In one case with us, we had a brand new aircraft bailed back to us and it spend it's entire operational life as a test aircraft and as a chase bird. By the time we finished with it, it was not suitable for use as a regular operation aircraft and ended up as a museum piece. When we shipped it out, it had virtually every modification within the production program that cad been produced for the previous 25+ years.