I have probably some of the oldest Glock mags around from my 1989 Glock 19. One is a 17 round and the other is a 15 round that came with the original Pistol. The bodies are not reinforced, I think some people here call them non-droppable. At the time I was told that the Austrians could not understand why Americans wanted magazines that could freely drop out of their weapons. These magazines have rarely been unloaded and the 17 rounded stayed loaded and lost in the trunk of my car for around 8-10 years. When It was found I it took it out and shot it with no malfunctions. After a good cleaning it and the 15 round mag has stayed loaded every since and that was years ago. Eventually I sold that Glock 19,
but I kept the mags and they are still functioning in my wife's Glock 26.