Difficult to exactly know for sure but let get it a try. Of course the part of the tag we see has been exposed to the sun for decades so that is not really trustworthy IMHO
SO we need to find some examples where the tag as been removed to examine the protected surface against the body or try and find examples where the finish is nice and has been protected by the dash pad not ones that have been left outside with the dash pad removed. Looking at just a collection of 70 VIN tags and not going through my complete collection of 70 pictures I have three at this time to offer for discussion. Of course we have the typical warning that its difficult to trust digit pictures projected on monitors but its a start
Contrast is the windshield opening semi-gloss black out application
As always hope this helps
Dearborn
Metuchen examples
Unknown how much exposure to the elements
From a wrecking yard example