Auction #93 Worldwide Air Post stamps and postal history, Zeppelin Flight items, philatelic rarities of the World

1918, two stamps with black overprint (type 5) on perforated 1k orange, one has upright overprint, the other one - sideways, both with full OG, LH, VF and rare, expertized by J. Bulat, stamps with upright overprint priced with ''-'' in the Cat., while sideways overprint is not listed, Est. $300-$400