Federal law mandated across the board use starting with the 1986 model year. As far as GM cars go, GM offered the CHMSL as an option for 1985 on the N-Body(GrandAm,Calais,Somerset),C-Body(DeVille,98,Electra/ParkAve) and A-Body(Celebrity,Ciera,Century,etc).
It's quite easy to spot a 1986 Corvette coupe,Camaro or Firebird. They have that little light pod mounted on the back of the roof. I can remember just about every car magazine that did a road test on one back in the 80's commented on how they look liked cheap add-ons or last minute fixes. Duh! If you think the bureaucrats are bad today guess who tought them. BO had nothing on Nixon when it came to creating agencies hell bent on trying to save ourselves from each other.
If you're really up on your Turbo Regal trivia you can easily ID any 84-87. I can proudly say I can anyway.