I have obsessed over this issue and that of primers and powder for reloading since the 1970’s. Rotation is the key in MY factory carry. My gunsmith/machinist/blacksmith/FFL (All the same guy, very well rounded) has suggested the issue of the degradation of the rounds due to excessive heat and the continued action of the powder in extra ammo in a vehicle. The post concerning the issue of oil contamination is certainly valid and as per most training either in published material and training. I have some 1943 ACP .45, government issue in box that I am proud of but not for use. I date all my ammo and components and the factory carry I mark with a black indelible marker across the case for identification purposes. In the days that I was in competition (Not very good, but did enjoy the sport) that is what we did to recognize our cases. Just had to have a different method. That was a few years back with a model 19, 15 and, really, a 28 Smith and Wesson. Wish I had the 28 and the 19. I will be interested in hearing from the folks on this post.