As this debate could rage on forever between those who have used the materials that cause it (or indeed just those who've witnessed it) and those who believe it's a myth, lets just run over a couple of things.
1. Yes, there is a bonding process even with the iPhone 7, of course there is. The display is bonded to the glass.
2. We have absolutely no way to know for sure which method Apple uses in their bonding process as they won't tell us that. But lets be realistic here, they are using some formulation of either LOCA, or OCA. (LOCA: Liquid Optically Clear Adhesive) (OCA: Optically Clear Adhesive, usually a tape or film.)
3. It is not at all impossible nor improbable for LOCA to be over-applied, or under-cured among other things, which can cause yellowing. This yellowing almost always dissipates before it ever leaves a factory due to natural exposure to heat and UV light, or a bit longer curing time of course.
However it's also possible for a LOCA bonded device which has a small degree of yellowing to be boxed, shipped and in a users hands before the yellowing has been eliminated by further curing. But small amounts of partially cured LOCA will usually dissipate and clear up as it is further exposed to heat and/or natural UV light.
4. There's also every possibility that yellow tints/blotches/clouding on any type of non-self emitting screens could be due to a vast array of factors. Badly calibrated, faulty polarisers (possibly as a result of over heating,) faulty blue pixels in the LCD panel, the list goes on and on and on. And of course most of these will cause a screen have a permanent issue.
5. We could go on for about another ten pages, but I need coffee
Most importantly, if you have a display you don't like the look of, either give it a few days or take it straight back. Your phone, your choice. Above all else you should be happy with it. These are very expensive little toys after all.
But let's not run around like headless chickens claiming something can't or doesn't exist because we've never seen it, when it's a well known factor in the industry. If you want to read about it, go ahead it's an interesting subject...Well, if you're that way inclined
Just search for LOCA yellowing and you'll find all you ever need to know, including why some prefer the non-liquid OCAs (hint, less chance of yellowing compared to LOCA.)
