the thing is people start measuring temps everywhere with nothing in the cooker, whether they are spot on or off 100° doesn't matter so much because once you start putting product in to cook it all goes out the window, they are convection cookers more than a radiant cooker, so when you disrupt the airflow the temps will be different, over time provided we do not sneak to many peeks the temps will even out for the most part across the whole chamber. I don't know how long that takes to happen but I have seen it in my Rec Tec when I used to watch temps.
It doesn't matter if the temps are off right to left or front to back, if you know that info then you are great use it to your advantage, if not you will learn if there are hot spots as you cook.
When I got my first one the Rec Tec I was checking temps and things and finally just said to myself this is how it works and went with it. When I got my GMG I never even checked grate temps just put food in and monitored the food temp and went with it. I now also have a pit boss vertical, no idea where the temps are on the different rack but I know that it seems to cook well when I use it, it is new so just learning.
Good luck finding anything that the temps are completely accurate 100% of the time, it doesn't matter what fuel you use it isn't going to happen, the burning and cycling will always have it changing.