But they don't show up in the in-game score page unless the kill was done in a bomber with pilot controlled forward firing guns.
ack-ack
This is not the case. What the in game score really shows are GV kills in bomber mode, no matter how they were made, and totally ignore plane kills. The website score card is exactly the opposite (showing planes only) and again, the way you did get your kills didn't matter.
I checked that out repeatedly.
See my current score for example - I killed 28 planes and 2 vehicles (1 in the Mossie XVI and one in the Lancaster). None of this kills was made with forward firing guns (the tanks had been bombed). And the website score shows 28 kills (the planes) while my ingame score shows 2 (the GV).