ORIGINAL: Capt. Harlock
It's a bug. The sqn assigned to the CVE conversion is used to early.
Now that you mention it, the A6M5 doesn't appear until mid-1943. Even if there were carriers in the area, those planes shouldn't have shown up.
"Availability" is not a single setting in the data file.
For an airgroup, the choices are base location (active now), ship location (active if the ship is active, otherwise active when the ship activates) or turns to arrival (applicable only to land based airgroups). An airgroup having an aircraft under these settings does not make the aircraft avaiable to other airgroups on the aircraft change menu or available for produciton on the factory change menu.
The aircraft data file has entries for available or turns to arrival. When available the aircraft appears on the factory change menu. When there are aircraft in the pool, it appears on the airgroup aircraft change menu.
When a ship is active, any airgroups assigned to it are active (see above "active when the ship activates"). So even though Chitose is not yet a carrier, and its airgroups have aircraft that are not yet available for production or selection by other airgroups, those aircraft are active becuase the ship is active.
Another example of this is that in some scenarios, Essex Class CVs activate with F6Fs before they can be selected for produciton. The reason is the airgroups are assigned F6Fs, the airgroups activate with the CVs, and activation of an airgroup with a particular aircraft does not over ride the aircraft data file setting for turns to arrival. All dates must be coordinated for availability to work as is appropriate.
The only interconnection among arrival date for an aircraft, activation of a factory to build it, and airgroups arriving with that aircraft is that aircraft arrival date will prompt the opening of a factory if one is assigned to produce the aircraft. Nothing else is connected.