I agree with John, the bottom of the hood has been repainted.
...that certain colors did not get the black-out treatment due to an enamel/lacquer mismatch
There was no issue with the types of paints. They only used lacquer. And the blackout of the firewall did not vary by model, every car should have gotten it, regardless of color. The blackout was to make the firewall uniform.
Can you post pics showing this?
Not uncommon to see some body color on the tag and the top of the firewall. The firewall blackout didn't always cover the top edge. I'm interested in seeing any pics of a car having color on the main part of the firewall.
I know of one car that did have green on the firewall. A silver 69. I need to ask for some more details on that car.