ERROR South Dakota 1975 Resident Antelope missing date & SN SD-A18a MNH VF ZAYIX

1975 South Dakota SD-A18a Error MNH VF 

Resident Antelope Hunting Stamp Missing Serial Number & Date with comparison normal stamp

There is no visible date or serial number ink but a faint impression of the strike by the press is visible under magnification.

Not listed in Cotton Catalog, 2nd Edition