Watch List notes:

Kushano-Sasanian. 3rd Century A.D. AE unit (16.68 mm, 1.67 g). Royal portrait / Royal portrait. Unpublished. aVF/F. Very Rare, possibly unique. 

Ex William F. Spengler collection. 

This notes on this coin by Spengler indicate that this was either a mint error or a special issue.