Ah, so that's it. But, where did you find out whether a panel seam is flush or overlapped? Wouldn't that require either visiting a museum with a P-40 in it, or a comprehensive set of P-40 close ups?
Overlapped panels are rare on WWII birds, aren't they? Though now that you bring it up I'm sure the panels in the nose of the B-17 just aft of the bombardier's plexiglass are overlapped....