Here's the scoop guys...
I've only seen '72 Chevelles with black-backed mirrors. As far as I know 1970-1971 were the chrome-backed mirror years.
As far as legal issues...
Well, the thing is most if not all restoration suppliers have "chrome-back" mirrors, however, they are actually ILLEGAL to use on a car driven on the road
Look carefully in most parts suppliers catalog (in fine print of course or in parenthesis)It mentions these are illegal.
Here's why: The reflections caused by oncoming headlights shine off the chrome on the mirrors and cause distractions.
I've never witnessed this being a problem, however I've never seen a '70-71 Chevelle coming towards me at night with my headlights on so I don't know how much of a problem this is.
It may just be the manufacturing of the repros, or ALL mirrors with chrome backs are illegal, but if your car still has it (like my '70) perhaps were "protected" by some "OEM clause". I don't know.
Anyone care to add?