Uh huh. Whateverrrrrrrrrrrrrrrrrrr.
I've been building models for 32 years and Testors Dullcote will yellow without exception given enough time. (Yes there are those who claim it doesn't. I haven't met anyone in person with that experience, particularly over white or light grays.)
It is my belief that more coats of the stuff one uses the more likely it is to yellow. That's what it does. (EDIT IN: He said he used Testors Acryl Flat, not Dullcote, so my speculation is irrelevant.)
The chemical properties that make it dull also cause it to yellow. As yet I don't think a single dullcote has been made that doesn't have this problem. (I have some Gunz-Sangyo that people claim won't yellow. I haven't had any on my models long enough to know if this is true, but on my test parts so far, the Testors has yellowed and the Gunz has not.)
So stick it.
My bad. I misread your post. I haven't used this stuff at all. I gave up on all Testors clear coats years ago. I contend it isn't the decals, though.
I have some of his that have been on my models and in the sleeves for years. No problems. But this does make me want to try an experiment with a test part, his decals, and Dullcote, Acryl Flat, and Gunz to see how they react. Might be interesting even if it takes years.
Heat and humidity are not the problem. UV is. Even in cold dry areas the sun through the windows is enough to cause all sorts of damage.