this is a topic you're going to get a lot of different experiences and opinions on. here is my experience.
Pistol brass in general can be reloaded many more times than 6. Glocked brass are problematic but not all Glocks do that. I believe this is a defect in the barrel and it's the single most compelling reason for my dislike of Glocks nowadays. I'd chuck those when I find them. I believe the over stretching of the case head area weakens the brass and next time it may not hold the pressure. And the 'donut'ed' case head causes reliability problems.
I'm more concerned with the straight wall case rim's health for reliability reasons. Extracted too many times causes rim damage. bad rim can mean feed & extraction problems. Primer pocket gets loose with higher pressure loads but that's mostly rare in pistol cases.
Rifle brass is more complicated. the bottle neck shape has much more room to stretch during resizing and 'work harden'.
During resizing, you're really stretching the brass into shape. the brass mass doesn't change. so if it stretches, it means somewhere is getting thinned. The case head area not supported by chamber gets stretched thin. which is why 'case head separation' and loose primer pocket. both situations can cause hot gas and/or debris or a flier at the least.
here is 1 factor most shooters don't see, chamber quality. the more room a chamber allows the brass to expand length & OD wise, the more stretching of the brass during resizing. the more full length sizing you do the less brass life you'll get.
I've see chambers large enough to cause case head separation with 2 firing of new brass. this is also why a 'match chamber' and neck sizing would allow for longer brass life.
My FN A3G, Savage 10FP have less than .001" head-space tolerance and the diameter of the chamber is at a minimum. The brass i use in them are loaded more than 10 times without problem signs (mostly neck-sized).
My old Ruger M77 30-06 would start to cause case head separation after 5 reloads of the same fire formed neck size brass.
work harden - brass gets brittle the more it's pressured during firing and sizing. you'll see split case mouth, case rupture when this happens. which is why some reloaders 'anneal' their rifle brass to normalize the neck tension and extend brass life. work harden can happen to both straight wall and bottle neck cases.
there is not a hard and fast rule how many times a brass case can be loaded but we know its life span is finite. If you reload, pay attention and learn to watch for pressure signs, brass fatigue signs for safety.
NRA Certified Pistol Instructor
Don't count your hits and congratulate yourself, count your misses and know why.