OP, I did not see your report of how your brisket turned out in the end with minor temp discrepancies.
I will reply to you and add my opinions in detail for any future readers who may be concerned about precise temperature measurements that may read this thread later and who might like to consider my opinion.
I see your frustration with thinking your external air on your temps and IT temps might not reading exactly correctly and humidity variances. I question if that is in fact reality important. First I have opinions of reading temps exact. I came out of the process controls industry where +- a few degrees could be a disaster with heated flowing plastics etc. I do have an opinion of several years of smoking stuff and learning from this site for my use and putting on several 30 or so people events couple times a year. We all have opinions of what parts of smoking meats are important to us that works for us and our equipment that over time let us produce a good product. I have some general thoughts.
One of them was my Dad staying up all night drinking Slitz beers char-coaling a big Brisket looking chunk of meat on a three legged charcoaler with a small fire using two small long screwdrivers to turn the meat frequently and to tell him when it was done in the late 1950's.
Guess today he would be considered a Red Neck, back then he just somehow found a way to make things work. Ha Ha We ate well growing up.
1st above all, you need to never put yourself on a time frame position where you might have a tribe of hungry angry people with forks in their hands looking at you and you knowing your meat might not be ready. Yesterdays perfect sliced brisket reheated in a crock pot or a foil pan in the oven with a little beef broth might be even better than just after you sliced it fresh. Smoke flavor gets washed even deeper than surface.
Basics, during smoking, you have the air surrounding your meat above the desired IT core temp you might need for it to be tender for what ever that chunk of meat IT needs. You can do that slow or faster depending on temp, bark or skin (chicken) will be affected.
Research here will show people like me doing briskets at 225' low and slow most of the time. I can usually guess approx timing (+- 3-7hours) while some here report pushing even up to 350' to come out with about the same results but a little tempermental. So what if my 225 is really 237? Or 250? Or 221? Only the amount of time it takes for my IT to get to "poke done"
Like the comments above, wait till the IT probes tell you it is at least 200' to start poking. At that point nothing else matters what happened before, 200' then 275', 350', open the lid 10 times or none, etc. IT of your meat is a general indicator, but really does not care how it got there. That chunk of meat will be done when it is done. Poking is the only TRUE indicator.
For me 200' is just the starting point of it letting me know it is time to start poking to look at when this chunk of meat might be as tender as I would like. Poke tough, add an hour, repeat till I am satisfied. A little stiffer poke some parts for slicing, more than butter feeling for chopped. Half way in between in different places for some of both. Could be 202' might be 215", several hours difference. Poking is the only way to tell. Every chunk of meat is different and it takes a little bit of practice and experience. Throw in two identical looking chunks of meat, pork butts for example and they rarely come out at the same time. Especially in the stall at 170 or so. One will hold longer. The other might even go down in temp a few degrees or stall longer for a while.
I have used dual wired probes to wireless receivers over the years. Like your kitchen oven, heat cycling on and off in the smoker, fuel feed, opening the lid, will happen. Yep, try to keep your smoker temp keeping air around your meat close to your desired temp, but I do not consider it overly critical in any way. Yep if you let it get way over temp for your situation, you will have some crusty bark. If you let it get it way under, your smoke time will take a little longer.
Myself, I have tried water pans and other items, really can not tell much of a difference to make it worth while with the airflow involved. Biggest factor of how crusty the bark is would be outdoor humidity and excessively high temps without spritzing a lot to keep the meat wet to slow bark crust or wrap in foil after smoking up to about stall time if you do not want much bark. Rainy days and most summer days in Oklahoma, humidity is high. Sometimes dry days I am a little more crusty. Many people will wrap in foil at or before the stall to prevent having a dry crust during the rest of the smoke if it is not desired.
Sometimes on a "flat" the tip gets very thin and could dry out. I fold it over, make a half way through cut, and secure with toothpicks. It now becomes a thicker piece of meat to not dry out as much.
If you have reached the soft poke temp for that chunk of meat, I wrap in foil to hold in the juices, wrap in towels and let it "rest" in an ice chest 1-5 hours. (Not planned, but the 5 hour one was still 170' to slice and was great.)
After some experience, you might find that some of the perceived "critical" items can be resolved by not worrying too much about the parts that are not really important.
Good Luck to you. Practice frequently and keep posting results as you go. We are all still learning and striving for our next smoke to be even better.
