Some headlight housings, such as those on my now-extant 2002 BMW 530i, aren't coated at all. I don't know about the Camry, but it shouldn't matter much because the coating (if any) is very soft and would be so badly damaged it should just be removed.
My car had the factory Hella Xenon lights, and at 125,000 miles (much of it highway) the lenses were quite cloudy and the focus of the beam was gone. There were some very deep pits from small rocks, no buffing ball or toothpaste was going to get the surface clear. Here's what the right side looked like:
I went to the local chain auto parts store and got bonded abrasive (silicon carbide) sheets in 400, 600, 800, 1000, 1200, 1500, 2000 and 2500. I filled two 5 gallon buckets with clean water, and did a double rinse with each progressive grit size. By hand, it took about 3-4 minutes for the first, making sure all the biggest pits were out and the new scratch pattern was all going horizontal. Each successively finer grit took 2 minutes or less, going in the 90º away direction with each. It's very quick (hey, it's plastic), and it was so easy to see when each was done because the lay was now changed. This was how it looked after the 800 grit:
By the time I got to the 2000, it was getting really hard to see the lay at all. It was that good. After the 2500, I did a quick buff with my finest buffing compound (Menzerna SuperFinish PO106FA) on a soft 5" foam pad on my Porter Cable 7424 random orbital polisher. That last step perhaps wasn't needed (was done after the photo), but it really made the lenses look as though they'd just popped out of the mold.
It really works, because the new owner of the car posted photos of it on a BMW website a year and 17,000 miles later and it still looked great. I've seen those "kit" results look back-to-cloud after a matter of weeks or months.