I bet 8 year old promags wouldn't work. Pretty much like factory fresh promagsI have a bunch of cheap polymer SWT mags from Sportsman's Guide that have been loaded and forgotten about for eight years (bought, loaded, and stashed them away in March 2015). I just found them at the bottom of a bin while reorganizing my gun room. Threw a few in a range bag and they functioned without problem. No cracks or any other issues with the lips.
Not gen1 PMAGs I realize, but eight year old rando plastic nonetheless.