My 68 GTO was suede finish (0% gloss) between the dash pad and the windshield. Lower dash areas we're 30% gloss. Supposedly GM did that to reduce windshield glare - would imagine that was a corporate decision and applied globally to all platforms.

My 68 GTO is the same exact...

The 70 Nova def had suede finish on the dash top, regardless of color. I don't believe the VIN plate was painted with a different finish though....

I just looked at my unrestored 70 Nova which has a black interior and it look's like the top dash black color is different from the vin plate color black. Look's like the dash was painted first, then the vin plate which is black was added after. There is a different shade of black between the two. Dash with suede finish and the vin plate not...

Not unusual. The dash was painted long before the VIN tag.

This is quite possible, most of the cars we see today have been Armor All'd to death and the original finishes are tampered...