brockage

If the mint worker did notice the brockage, they had the option of restriking it.

One extremely rare error is the brockage.

A brockage is when a mirror image of a coin is struck on both sides of the planchet.

The second coin is called a brockage, but the first is sometimes considered a variation of a brockage.

Likewise, a type collection might focus on an unusual design feature such as coins with a hole in the middle, coins that are not circular in shape or coins with brockage.

In coin collecting, brockage refers to a type of error coin in which one side of the coin has both the normal image and a mirror image of the opposite side impressed upon it.