Well, this will probably earn some flames, but here we go:
You only receive credit for a kill if the plane you shot down remains within your visual range.
This has a historical precedent, as confirmed kills were only rewarded when someone actually saw the plane go down. Anything else was generally only considered a probable (in the US forces. IIRC, the Germans didn't award "probables." It was either a confirmed kill or it wasn't).
If you damage an enemy aircraft (fuel, engine or wing) you don't get credit for the kill when he bails or augers if you don't stay within visual dot range. This would help cut down on incidents where an enemy aircraft is completely flyable, you saw his wing off, but someone half a sector away gets the kill instead because he caused more damage to the component than you. If he's out of visual range he still gets the death/bail/captured, but you just don't get credited with the victory. Because frankly, it's silly to put some holes in a plane and fly away, only to receive another kill three minutes into your landing approach.