It happens with quite a few museum aircraft, and not just in the U.S. One of the big ones is the inclusion of the radio antenna wire, through the hood to the fin, on P51Ds restored to represent 8th AF machines. They didn't have it - the antenna was a dipole inside the mast, for the VHF radio. The flap hinge line was left bare mainly for two reason; to avoid any fouling from paint scratching or wear, and because it would be in the 'up' position probably when painted. Plus of course, the paint would wear off anyway, as the flap indicator panel often did.