Many collectors long thought the blue plane portion was printed first, thus it was actually the red frames that were inverted. In fact, the frames were printed first and it is the planes that are upside down. In examples where the plane is so far off center that it overlaps the frames, it can be seen that the blue ink used to print the plane lies atop the red ink used to print the frames. The Smithsonian's National Postal Museum offers two explanations for how this might have occurred: either a sheet of printed frames was placed in the press upside down for the printing of the plane; or the printing plate used to print the planes was mounted inverted within the printing press.