There was a really good thread on this a while ago.
Finally found it!
https://www.yenko.net/ubbthreads/show...p;Number=13895
For the low-volume COPO, Chevy could piggyback off of the Vette certs. But for the RPO engines.....
From JohnZ:
ALL big-block '69 Camaros (L34/35/78/89) had A.I.R. systems, regardless of transmission application. EPA emission certification was done not only by powertrain, but by carline application, vehicle weight, aero drag, and coast-down horsepower testing, which created many variables. Every different situation required full EPA certification, including 50,000-mile durability testing, and Chevrolet apparently decided that rather than go to the time and expense of developing and certifying eight different low-volume Camaro big-block combinations, they'd go with only four, that they knew would pass and certify with A.I.R. For the high-volume passenger cars, however (Impala/Caprice), which were built in Nine assembly plants at 7,500 per day (vs. only one plant of Camaros when you factor out the Firebirds at Norwood), it made sense to certify high-volume passenger car combinations as much as possible without the added per-unit cost of the A.I.R. system, so many full-size Impala/Caprice big-block applications were developed and certified WITHOUT the A.I.R. system. I had a brand-new '69 Caprice 2-door hardtop with the 427/THM400 combination, and it didn't have A.I.R. either. Full-size cars and Camaros were totally different certification situations.