Ringed barrels& Excess headspace Cont'd

Evaluation of the safety and accuracy of ringed barrels or excess headspace ARE scientific studies and engineering test jobs because of the number of technical variables involved. They also involve test and measurement equipment beyond the scope, inventory & knowledge of the average shooter/ handloader.
Safety testing by definition means testing to limits or destruction.
Implicit in all this is that safety measures must be observed during the testing.
As to the matter of strength diminishment of barrel steels suffering permanent deformation; it's a question of alloy, hardness and percent deformation. Deep hole drilling of barrels results in a goodly number of curved bores. These barrels are bent to straighten the bores and then the outside diameters are turned to be concentric to the straightened bores. As a side note: An M-3 greasegun barrel was developed in WW2 with a 90 degree bend for shooting around corners.
In both the button swaging and hammer forging rifling methods, nononsense about it, barrel steel is stressed beyond yield. It's deformed by high pressure or hammering. This deformation is on the order of a .010" decrease in bore diameter for hammer forged barrels. Many ringed barrels I've seen were on that order.
So the change in barrel steel properties for small deformations isn't meaningful strengthwise, but shooting a high pressure round may create some issues at the ring. Just what and how much remains to be defined. I'd welcome seeing properly conducted tests since I've never seen or heard of a barrel burst or gun blowup resulting from a ringed barrel. To make sweeping statements on these matters I believe is not technically sound. I'm really not interested in subjective opinions of ten "experts" or any more urban gun legend and prefer to operate on hard empirical data: Just the facts, man.
A proper assessment of these conditions is very technical and not for a backyard mechanic, which I tried to convey gently.
Excess headspace can be meaningful on a rimfire or with hot loads in the old folded head cases or on older improperly made brass having soft heads. Brass can and did blow out and injure the shooter, sometimes damaging a gun. With modern centerfire cases in modern guns I believe the danger is overstated and too general.
If headspace is growing that's cause for concern.
If you're a "Kick the tires and light the fires." kind of guy, then
stick closely to the cited SAAMI recommendations.