DOUBLE- AND MULTIPLE-STRUCK COINS
When a blank planchet is struck by the dies, the normal
procedure is for the feeders to eject the struck coin out of the collar and into a chute. If there is a malfunction and the struck coin isn't ejected, it may receive a second or third strike by the dies. A multiple struck coin can happen in many ways and have many combinations of errors.
Images courtesy of Byers
Sacagawea $1 Struck 18X in an ANACS
holder (illustrated above).