For the purposes of the Axis vs Allies or a rolling planeset environment, I'd say we would need to pick a date at which the aircraft was in significant service. Using the Spitfire Mk XIV as an example, I would say June or July, 1944, make it 3rd quarter of 1944, would be fair. A single squadron equipped with them in January, 1944 and not seeing any action at all until March, 1944, just does not seem to meet the standard needed for an aircraft that will, theoretically, see very wide usage in the game. The Fw190D-9 I'd make available in October, 1944, say 4th quarter of 1944. For the Me262, we'll set 3rd quarter of 1944 as well. Even though the Meteor Mk I technically entered service before the Me262, I really wouldn't consider the Mk I a valid addition to AH, it is more of a prototype than production version. The Mk III on the other hand could be fairly set at the 1st or 2nd quarter of 1945.