I couldn't agree more.  I also once found a 1911 mag that had been loaded forever, fired all seven without a hitch.  I have several S&W 4006 mags that have been loaded for approximately 10 years, fired one the other day, again with no problem.  Saw plenty of brand new GI M-16 20 round mags that would not work with over 18 rounds in them.  It all depends on the mag...
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OBG