1981, 18¢ Flag & Grain, imperf between, vertical pair, o.g., never hinged, bright and fresh, Very Fine, despite the woefully low catalog value of this newly discovered error, this pair is reported to be unique in the 15th edition of the Datz catalog; with 2008 A.P.S. certificate. Scott No. 1890c; $550  Estimate $750 - 1,000. $0 (Image)