Airmail stamp for Boork-Brück, perforated, corner margin copy top left, in perfect condition mint never hinged, only issued 1. 000 pieces - being a corner margin copy in this preservation rare, first German airmail stamp the only a few days was used, photo expertize M. Brettl International Association for Philatelie Experts (2016) : "In finest perfect condition, mint never hinged, without hinge. ", Michel 1. 400. (free of premium for the decorative corner margin copy!)