The first legislated exhaust (tailpipe) emission standards were promulgated by the State of California for 1966 model year for cars sold in that state, followed by the United States as a whole in model year 1968. Also in 1966, the first emission test cycle was enacted in the State of California measuring tailpipe emissions in PPM (parts per million). The standards were progressively tightened year by year, as mandated by the EPA.
By the 1974 model year, the United States emission standards had tightened such that the de-tuning techniques used to meet them were seriously reducing engine efficiency and thus increasing fuel usage.
From
So it is not the requirement of when the car was manufactured as I am pretty confident vehicle in CA manufactured from 1968 throug h1974 are currently exempt even thought they had some smog standards. I do have a very vague memory of my parents needing to have a 1971 vehicle smogged. I don't know what was involved. It may have been a visual inspection that the was no after factory modifications.
By the 1974 model year, the United States emission standards had tightened such that the de-tuning techniques used to meet them were seriously reducing engine efficiency and thus increasing fuel usage.
From
Vehicle emissions control - Wikipedia
en.wikipedia.org
So it is not the requirement of when the car was manufactured as I am pretty confident vehicle in CA manufactured from 1968 throug h1974 are currently exempt even thought they had some smog standards. I do have a very vague memory of my parents needing to have a 1971 vehicle smogged. I don't know what was involved. It may have been a visual inspection that the was no after factory modifications.