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There is also a difference between being UV resistant, and having UV blockers. A UV resistant coating will resist yellowing and degradation of itself, but it doesn't prevent the UV from passing straight through to whatever is underneath.
You can witness this with unpainted Kevlar laminates, as Kevlar is also highly UV sensitive. After a few months in the sun, Kevlar will start to turn brown. This isn't the epoxy yellowing, it is the UV passing through the epoxy and degrading the Kevlar. To protect it, you need to prevent the UV getting to it, which is why Kevlar laminates are very often painted with a solid colour.
But the automotive and marine industries have been dealing with this for years, which is why automotive and marine 2k coatings tend to have the best UV blockers. And even within those industries, some products are much better than others. House of Kolor Show Klear is the absolute best I have found. Ive got a couple of test pieces that have been coated and sat outside in the Aussie sun for the last 2 years with still not a sign of yellowing. Other coatings and uncoated parts won't last a month of constant exposure to our summer sun without showing signs of degradation, so it is very impressive.