PART III. Die Installation Errors:

Mules: 

Temporal mule, 2000 Macedonia 1 denar muled with

obverse die used 3 previous years

Definition: Mules are coins struck by mismatched dies.

Shown below is a 2000 Macedonia 1 Denar. The reverse of this special, 1-year issue carries an ornamental cross.
The obverse is supposed to show a Byzantine coin. This mule, however, carries the ordinary 1 Denar design that was used in 1993, 1997, and again in 2001. It’s possible a 1 Denar design from 1997 or 2001 was mistakenly employed as the obverse die. It’s equally possible that a leftover special-issue reverse was mistakenly substituted when the normal design was re-instituted in 2001.