Hey! I finally registered so now i can add my 2 cents.
So i have noticed this happen to me a few times. However, the times i would not receive the claim report were the times that i shot an enemy craft up really bad and let it fly off (usually because i ran out of ammo). then 5-10 minutes later i would receive the "plane destroyed" message. At the end of those missions, it would not give me the option to fill out a claim report. After a couple of times of this i decided i was going to follow the beat up enemy craft trying to flee the field. After about 5 minutes it became really obvious that this guy was not going to crash due to the 100 or so rounds i sprayed his plane with. So i broke off my pursuit as he was crossing back over his lines. again, maybe 10 minutes after i disengaged, i received the "plane destroyed" message.
Something must have happened to the plane after he was far enough away. My original thought was that he was shot down by someone else. But for it to happen to every plane that i get a couple bullets before it flees is a little unlikely. So my next thought is that it must be that the plane has landed and the system decides that it has been "destroyed" similar to how if you land your plane at the end of a mission it quickly despawns you.
maybe? well at least that's what im telling myself when i end a mission without a claim report. (THo, the frequency of this happening to me is much less since my gunnery skills have been improving)