yes. when the UV protection is compromised it's apparent that some lights can experience failure throughout the depth of the material, including the inside.
and though i don't have science to back it up, i believe that the light optics (reflectors) can probably reflect UV energy that isn't blocked by the failed UV protection on the outside and help degrade the plastic faster that you'd think from the inside. factor the thermal expansion/contraction during repeated use and i think the material becomes even more brittle which certainly doesn't help things.