Thats also the reason for my caveat in my description when posting the drawing.
Now as then I strongly belive, it springs from 'artistic lisence' (which is a nice way of saying 'a figment of someones imagination').
Not that I know as much about Japanese markings as you do, but merely because of the circumspect comments (or lack of any comment) to the drawing.
A theory; maybe few if any documentation/photos ever surfaced in the West of the F4U in Japanese guise and thats the reason, that this drawing came about.
It might be known, that a/the F4U was captured, but there were no photoes/documentation, so they just slapped somehting on the outline of a Corsair.