IDK why they care as long as it passes the exhaust sniffer test...
About 42 years ago, I went to state inspection school here in Louisiana. I know that we are not near as strict as Cali is, and again, 42 years ago, things were a lot more laxed than they are today, but even way back then, the law said, if there are repairs to a vehicle that then need to be to OE spec. If not, then the vehicle is to be rejected from state inspection. It is to have a big red rejection sticker put on the windshield where the inspection sticker would normally go. This sticker allows the owner up to 1 month for repairs. At that point, the vehicle has to go back to the same place that issued the rejection sticker for reinspection. Replacement parts must be as the vehicle was when it left the mfg plant. So for example, tire size needs to be of the same basic size to fit the vehicle. The brand of parts were not what is important. What is important, is that replacement parts are of the same as that originally intended for that vehicle. Tires can not extend past the fenders. A truck can not be lifted so that the headlights are above the mfg height for that vehicle. So they could not be higher than the normal 4x4 headlight height. That is just a few examples of what we were told. At that time exhaust could be sniffed for emissions, with an exhaust probe, but that was not necessary in our area. No one here followed that, as strict as we were told to then and still don't today, but the laws are there. Today emissions testing is only required for the Baton Rouge area. There they require a scanner test of the ECM. And again, we are talking about Louisiana, not California.