I have to agree with adamlbiscut. I think you may be dug in a bit too much. That being said, you’re right that tolerances should be followed but these are mass produced devices. It’s impossible to guarantee perfection. It’s not all robots making them either so human error comes into play. There’s a lot of human interaction so flaws are bound to happen. Plus as I mentioned originally, they usually use mounts that the screen sits in to keep it uniform on a production line but if the mount gets dropped and is damaged, has a small burr on it, or something like a hair or piece of dirt gets between the screen and mount then it can cause the glass to not lay flat and will cause this sort of thing.
So yes, they should follow their tolerances and they do. But mistakes happen. No one’s perfect. Not even Apple.