The “legal range” of pressures was just Wilsons recommended pressures for the care and use of a football, instituted at some unknown time before 1940. It was about giving players a ball they could use, not about anything else.
Starting with pre-game measurements at 72F indoors, the PSI of footballs varies by almost 6 PSI between the warmest games and the coldest games each year, and in the 50F range, *varies* up to an additional PSI according to how wet it is. Balls on top would also be notably different pressure than those on the bottom if hit by sunlight or near the warmers. Heck, balls held by the ball boy or ref would vary by more than the NFL was actually quibbling about, depending upon how long they held them.
None of that is actually in opposition to the Wells report data and formulas - they just were very dishonest about what they found, and what they were telling you that graphs represented.
No one cares except as a gotcha.
See Addendum B in the following for some nice graphs on historical pressures.
https://cbsboston.files.wordpress.com/2016/05/physics-professors-deflategate-filing.pdf
The problem with decreasing pressure is due to balls being inflated indoor where it's warmer.
The solution:
Take the machine that inflates the balls and all the ball completely deflated; without any residual air.
You take the machine and you lay each ball on the turf at least 1 hr before the same so they all reach the game ambient outdoor temperature.
After 1 hour or two or three, just before the game when the inflating machine and the deflated balls are all at the same outdoor temperature you then inflate all the balls to regulation pressure.
The only minor questionable variable I see is that over time the inflating machine might get warmer the longer it is running.
OPTION 2:
If the NFL allows teams to use their own balls there's another solution.
Each team deflates their balls and leave them on the field with the inflating machine so they all reach the same outdoor temperature.
Each team takes turn alternating inflating their own ball. However, the opposing team then tests the pressure on each.
If the opposing team ball is found to be off the team checking the ball can inflate it to the proper level and then the other team can measure the pressure.
Each team would keep the other honest.
Once the balls are properly inflated a neutral party maintains possession of the balls until needed so no one can stick a inflating needle to release air (although that could be done ON the field DURING play by any player hiding an inflating needle on their person).
Pressure in PSI is not the only factor, when it comes to temperature based effects. The material(s) the football is constructed of change properties considerably with temperature. Hardness, stiffness, and likely internal damping of the materials all increase with decreasing temperature, which would tend to (mostly) counteract the pressure drop. (The damping change might add to the pressure drop in creating a less “bouncy” ball.) I would not be surprised if “operationally” those “materials” factors are more significant than the effect of the pressure drop.