Yes you are right or so I have been told. I also have seen more than one car with it trimmed in argent.
I knew that when I painted mine and prefer the argent on top to breakup the blacked out tailend.

I also still have a original 71 RT 340 tail light bezel from a car I wrecked in 1978 that was original, that has the argent on top. I still have it and kept it and didn't use it on this clone. I can take pictures of it, it has the top edge trimmed in argent. So that's why I painted mine that way because my original was like that and I like it better that way. Still not saying it's right or correct.