In researching WW2 aerial campaigns (and others) I find that pilots of ALL nations often over-claim kills by a factor of 2-4. I arrive at this figure when from reading comparisons of records for the same mission from both sides. In most cases, each side accurately report losses, but seem to have claimed more kills than the other side lost by a factor of 2-4 (some cases better and some cases worse).

This is not to say that anyone is necessarily cheating on purpose or for propaganda purposes (these are battle reports, not press reports).

• In the heat of battle, exactly what a given target did or exactly who shot at it may be hazy.
• Two (or more) pilots may target the same aircraft - and both claim the kill, not being able to tell due to angle through a furball that they were both shooting at the same aircraft.
• A target that is not actually followed all the way down to the ground and seen to crash may have pulled out and returned home battered but alive. Smoking and diving aircraft may just be trying to get away.

This is not meant to be an exhaustive list of possibilities. My point is to read pilot's claimed kills with a grain of salt.