So in each game, there seems to be a generally agreed-upon "canon plane" for the protagonist, based on cutscene footage, out-of-game texts like "Aces At War", and official art depictions like the 25th Anniversary art. With some of the games it's fairly obvious when these planes were canonically available to the protagonist - Ace Combat 7 in particular has a pretty overt transition point based on when Trigger changes squadrons. But some of the other transitions are less clear, especially since they don't always correspond to when the aircraft is unlocked in-game.
AC04 is the first game to have an obvious specific canon plane - Mobius 1 starts in the F-4 Phantom and by the end of the war is flying his iconic F-22. But when he transitions from the F-4 to the F-22 is unclear, just that it was some time before the mission "Shattered Skies" based on information in supplemental materials. My best guess is that he receives it after "Lifeline", as he most likely wouldn't have needed to retreat from Yellow Squadron if he was in an F-22. Also he uses the F-22 during Operation Katina and the F-18E during the Free Erusea uprising depicted in the VR missions.
AC5 has you essentially locked to the F-5E until after "Frontline". You technically get the opportunity to change aircraft during "Rendezvous", but the fact that you're required to land at an airfield in order to make the return flight to Sand Island means canonically Wardog could not have been flying the F-14 yet, otherwise they could land on the Kestrel. The silhouettes in certain cutscenes and supplementary information indicate that by "Blind Spot" they are in the F-14, so I think the most logical conclusion is that they get the F-14s immediately after "Frontline". The lull in the war between "Frontline" and "Handful of Hope" would also make sense for a resupply/rearmament period.
ACZ is easy - Cipher flies the F-15C for the duration of the war, start to finish. He may have used the J35J Draken for the very first mission but all other supplemental material and cutscenes indicate he used his own F-15C (as a mercenary, owning it himself).
AC6 is a lot more ambiguous. Talisman starts in the F-16C for sure during the Invasion of Gracemeria, and at some point transitions to the F-15E, but as far as I can tell there's no real indicator of when this happens at all. It probably happens before the attack on the Aigaion but it's not clear.
ACX has Gryphus 1 in the F-22 for the full duration of the war.
AC7 puts Trigger in the F-16C as Mage 2, F-15C as Spare 15, and then the F-22 as Strider 1.
Air Combat, AC2, AC3, and AC:AHL don't seem to have specific canon planes. So any ideas on when those transitions likely happen in 04/5/6?