VERY FINE-EXTREMELY FINE. AN EXCEEDINGLY RARE LARGE PLATE NUMBER BLOCK OF THE 24-CENT 1918 AIR POST ISSUE WITH BLUE "TOP" ONLY. ONE OF THE GREAT RARITIES OF UNITED STATES 20TH CENTURY PHILATELY.
The first printing of the 24c 1918 Air Post issue was trimmed so that the plate numbers at top, the right selvage and guide arrow were removed, resulting in a straight edge at top and right. Immediately after the invert error was discovered on one of the first printed sheets, the Bureau of Engraving and Printing officials decided to add the word "TOP" to the blue "Jenny" vignette plate and modify the perforating/trimming process, so that when new sheets were printed, the word "TOP" would appear in the selvage. This would help prevent more errors from slipping past BEP employees in the printing and examination process.
Only a small number of sheets were printed with the Carmine frame impression lacking the "TOP" that was added to the plate -- they are known as "Blue Top Only" sheets. Subsequently printed sheets from the modified plates have both red and blue "TOP" imprints, which are found on the vast majority of surviving plate blocks.
No plate blocks from the first printing can exist (other than the unique invert error plate block, with the blue plate number at the bottom of the sheet). Blue Top Only plate blocks are rare. According to Joe Kirker’s census, only 24 Blue Top Only plate blocks are recorded. This block comes from Kirker’s #4 full sheet (since reduced to this size).
Scott does not price the Blue Top Only plate block in Mint N.H. condition. Scott Retail as hinged plate block and Mint N.H. singles