E is for EFOs

Errors, Freaks, Oddities
EFOs Cinderella Stamp

"Errors, Freaks, and Oddities" refers to misprints, misperfs, and other stamp production errata. Perforations shouldn¹t run down the middle of the stamp; ink shouldn't be smeared or blobby; elements of the art shouldn't overlap — or be missing. Errors in design occur as well, such as on the notorious 1994 Legends of the West stamps, where the wrong Pickett brother was shown.

29c New York Stock Exchange Bicentennial inverted block of four
New York Stock Exchange Bicentennial error

Two panes, for a total of 80 stamps, are known to exist: 56 with inverted centers and 24 with missing centers. This corner block contains two of each, plus partial images in the selvage. United States, 1992.