My numbers are also significantly off, though I did track down at least one variable. I was once flying a Seafire over the location of a recently sunk enemy CV, and enemy PT's were still spawning. Unfortunately for them, they spawned within the automated gun range of my own CV and were quickly destroyed. I got credit for 10 kills this way, without firing a shot. But I later noticed that these kills were not computed into my ranking score, only my specific kills vs. plane stats. Which is only fair, IMO.