I have a theory to the reason why we get 'stem' flats but no supporting evidence. I'd like to throw it out and see if anyone agrees. (I have never searched the topic, so I apologize if I'm repeating)

Is it possible that the stem nut which holds the stem in place while inflating, can be tightened too much? In the past, I would tighten the nut down snug with the rim, but I've since changed my mind.

Theory goes, the stem nut gets tightened on a 'fully' inflated tire (say 100psi). After a given time, the pressure drops to 60psi, but the nut is still tightened to the fully inflated tire and the reduced pressure in the tire causes the rubber around the stem to stretch and weaken.

I would like to ask those who get stem flats, do you use stem valve nut? If so, how tight is the nut to the rim?