1875-90 1m deep green and scarlet perf.11 1/2 instead of 13 1/2:14 1/2, a proof that was sold by error at the post office and used with partial Heligoland double arc cds, very fine and extremely rare with very few used known; signed Lemberger, Grobe and Wollner; cert. RPS (2019) (Mi. €7'000). (Image)