1 Mark on 10 penny airmail with overprint \"Gelber Hund\", variety \"inverted overprint\", horizontal pair - as well the right stamp with overprint flaw \"Huna\", mint never hinged without any signatures, accompanies becomes these major rarity from a photo expertize Mary Brettl International Association for Philatelie Experts (2022) : \"the inverted overprint is very rare, issued only 200 pieces. Me lay so far from the overprint flaw only two examples before. As a pair IV K / IV F K major rarity, probable unique. The right stamp on the reverse side with traces the blue overprint colour. Both examples in finest, perfect condition. \"