There was a months long (maybe a year long) batch of bad screens both MCU and IC screens around late '16 and most of '17. Mine was replaced, and yellowed again. They figured out they could fix (bandaid) the screen themselves at the SCs with a UV light that covers the screen. Some screens took double/triple the time under the light than others. Some took more than a day. It was curing the material to prevent the yellowing. Some, I think, were not left under the UV long enough (hard to gauge the time necessary), so the yellowing returned. Left a bad taste in the owner's mouth when that happened. I don't remember exactly where it is, but you can go over to teslatap.com and scoll through his stuff. He bought a UV light on Amazon and did his own fix. I think he paid something like $30 for the light. Not all the SC's had the lamp for a while and some were passing the lamp around to other SCs, while they were testing the fix.
Someone is going to say their '18 or '19 also had the problem. I don't doubt them. Stuff breaks, less than perfect stuff gets pass inspection. It ain't a purrfect system. But stuff gets fixed. The effort to worry and complain can exceed the benefits to the mind and body to just shake it off and not be so serious. Ya know?