1930 6c Plane & Mt. Aqua, vertical imperf pair with a single line of diagonal perfs, from the unique sheet that yielded the few imperf pairs known (Scott $350), lh, very fine and the only one like this we’ve ever seen ! (Image)

1936 (June) 3rd North America Return Flight, long registered cover with “Quetzal” ovpt. franking on face (60c total, 5 diff stamps) and 6 more stamps on back (16c total), all tied on June 17, no transits but Lorch (Germany) bs (June 27), scarce as only a few were carried, very fine (Sieger 418 A, € 300+) (Image)

1937 25c Green, the important “missing quetzal” variety, an exceptional example with light cds, faint bend, very fine, 1986 PFC and signed Bloch, only a few known (Scott $1’100; only known as used) (Image)