Ten different flags that Americans carried as colonists and as citizens of a new nation were reproduced on one pane of fifty stamps. They were first placed on sale on July 4, 1968, at Pittsburgh, Pennsylvania, where the Allegheny Trails Council, Boy Scouts of America, dedicated its Flag Plaza and program and service center.
The series consisted of the Ft. Moultrie Flag (1776); the Ft. McHenry Flag (1795-1818); Washington's Cruisers Flag (1775); Bennington Flag (1777); Rhode Island Flag (1775); First Stars and Stripes (1777); Bunker Hill Flag (1775);Grand Union Flag (1776); Philadelphia Light Horse Flag (1775); First Navy Jack (1775). The ten flags were arranged vertically on the pane in the order listed above.
The stamps had an initial printing of 120 million.
Reference:
Postal Bulletin (June 6, 1968).