Hi everyone, so I thought I'd share my anecdotal take on the situation.
I had a launch day iPhone 12 Pro in silver and noticed a very yellow screen and a lower contrast compared to my 11 Pro, as well as fitting issues where the glass meets the stainless steel giving off a "peeling off" sort of look. In addition, I found scratches and dings all around the stainless steel out the box. It bothered me to no end but I figured it was normal since I noticed the same thing in the Apple store display units. The whole device just seemed not as premium when held in the hand and was disappointing but thought it was normal.
However, my sister ordered a new iPhone 12 Pro and the device seems much better built. The tolerance between where the glass meets the metal doesn't have that peeling issue. The screen has a much better white point, and what's more strange is that her device boots up much quicker than mine and doesn't have that weird gray glow during boot up. The device was manufactured in week 2 of January.
I then ordered a new iPhone of the exact same configuration (iPhone 12 Pro Silver) thinking that manufacturing has been quietly improved and fixed and when I got the device my hypothesis seemed validated. The device had no peeling my other device did and the white point was leaps and bounds better than looking at a piss yellow screen in my old launch day phone, and the contrast on the new display is gorgeous even better than my LG OLED TV. My older phone also had a weird green gradient on top which was gone as well, and what's even weirder is that battery life seems to be way better with this device (though that could just be due to a whole host of other variables). Another thing that alluded to a better build was that when I used my old phone outside there would be a weird reflection on the screen almost like there was a gap between the glass and the display that was warping the light. Also a lot of dust had accumulated where the glass meets the metal due to the looser tolerances but this one did not have the same problem. This was not an issue on my new device. This was manufactured week 3 of January.
I don't have pictures to compare the two since I have already sold the old iPhone since it was outside my return period and there was no way I was going back to that poorly built device after seeing a properly built device.
Now it may be a stretch but I think what happened is that Apple rushed out deliveries of the iPhone 12s during launch which led to lower QA on these devices, due to high volume of orders and the stress COVID had on manufacturing lines. Apple then addressed these issues later in production which included yellow screens and tighter tolerances. I think Apple should be more transparent about fixing these issues rather than addressing these quietly but I sort of understand it since having to replace the millions of iPhones they sold with new phones would be costly and not a difference everyone would notice.
If you guys are having issues with your phones you should try asking for an exchange since the newer ones seem to solve all these issues specifically ones manufactured in 2021. I understand this may not be possible for everyone but good to know nonetheless.