Never intended to leave the printing facility, stamp “errors, freaks, and oddities” or “EFOs” is a term that refers to all the kinds of things that can go wrong when producing postage stamps. An error can mean anything from just poorly printed to major design mistakes. Errors attract the attention of relatively few collectors and they can be among the most expensive stamps.
Any sort of production mistake that is repeated many times (whether just on one sheet of stamps or many) constitutes a stamp error ; the famous Inverted Jenny is the best known of these and now extremely valuable, resulting from stamp sheets being accidentally reinserted into the printing press upside down for the second color. The result was an invert error. It is also not especially rare for perforating equipment to malfunction and result in perforation error stamps.
Some design errors include wrong dates, wrong names, wrong pictures, and similar mistakes. A notorious example is the 2011 Liberty stamp error which shows the Statue of Liberty replica from the Las Vegas Strip rather than the original lady in New York harbor. Three billion of them were printed and sold. Color errors include stamps like the Treskilling Yellow which was meant to be green. Another well-known type of color error occurs when modern multi-colored stamps are printed with one or more colors missing.
Monaco stamp: The man’s left hand has five fingers and a thumb. Hubert Humphrey stamp: correct dates of his service are 1964 – 1968. Errored stamp show dates of service as 1965 – 1969.
A one-time printing misstep constitutes a freak stamp. Freaks include paper folds resulting in half-printed half-blank stamps, “crazy perfs” running diagonally across stamps, and insects embedded in stamps, underneath the ink.
An oddity stamp can be used for postage, but one glance will tell you that something is not quite right. The typical sort of oddity is misregistration on a multi-colored stamp. This can result in shirts apparently with two sets of buttons, eyes above the top of a person’s head, “moving” items and similar situations. These can be extremely common. The Canadian Christmas stamp of 1898, depicting a map of the world with British possessions in red, is famous for unusual color oddities that appear to claim all of Europe or the United States or central Asia for Britain.
Postal authorities generally take care to ensure that mistakes don’t leave the printing plant. Mistakes smuggled out by unscrupulous employees are called printer’s waste, not recognized as legitimate stamps, and may be confiscated from collectors. To be considered an error, freak or oddity, the EFO stamps must have been sold to a customer in a post office or by the postal department. Postal authorities may attempt to confiscate legitimately-sold errors, as happened with the original Inverted Jenny sheet, but usually collectors are smart enough to hang onto the windfall.