About 700 of the stamps were printed in error in 1918 with an upside down illustration and only 100 went on sale, however, it will be 22 months before laws will allow the box with the envelope to be reopened so the stamp can be checked.
The stamps carry a picture of a Curtiss JN-4 plane, known as a Jenny, which was used for training pilots in World War I and later became an airmail plane.
Broward County Commissioner John Rodstrom said he spotted the red and blue Inverted Jenny on a large envelope with two stamps from the 1930s and another dating from World War II but the envelope had no return address so the ballot was disqualified because it gave no clue as to the identity of the voter.
