Yes, planes are in the sunlight for 8 hours a day, 2 days a week for 1-3 years at the flying field.
Sorry but just because YOU don't think it is valid, does not make it so, you don't determine what is valid and what is not, and are not a ruler of who posts in this thread. I have posted no misinformation just facts from my experience as you have, it yellowed. I think your test is misinformation and not valid, slapping some on a piece of paper shows nothing.
BTW The topic of this thread is about finishing, not only finish cure epoxy but all finishing.
I used it exactly how it was designed to be used and it yellowed, Period.
For your enjoyment, a 20k "toy" crashing at 200mph
http://www.youtube.com/watch?v=MR4CntziBe4