Glenn
I think I have found another bug. I have attached a stock scenario file with one change. All I have added is the 601st Fighter Sqn. The unit is 'Not Available' from the start of the scenario and becomes available later on. The problem is the unit is taking losses from Air Combat even though it is not in the battle. I hope you can see the problem with this. If you play through a few turns you can check the unit in the air unit list dialog. You will see the unit is taking losses. It starts with 12 aircraft and in my example has been reduced to 9 aircraft after only a few turns, and its not available for operations. See attached files.
Actually you don't even need my test.scn. You can see the same problem in the El Alamein scenario. There are several Axis air units that start the game not available and they are taking losses before their available date.