The letter date code begain in 1968. Here are two sweat sheilds from 1969. Both from the same VEB 1856.
The diamond shaped sweat sheild was first used for 1982,. Apparently the old sweat sheild was last used for 1982.
Four varieties of the diamond shaped sweat shield. 1: MdI. 2: NVA, with Veb # and date code. 3: NVA, no Veb or date code, from a GST visor cap. 4: no agency markings, from a zollverwaltung visor cap.
Seems straight forward. MdI hats are marked MdI. NVA and GST are marked NVA. Zoll are not marked...
... this sweat shield is from a 1988 dated EM NVA visor cap. So what is my point? No point, I'm just making note of it.