Back in my Mil-Spec of the mid 80's, we came across some 1911 mags that were loaded and sealed in a tin. The date on the tin was 1965 (the year the ship I served on was officially released to duty). We opened the tin and took the mags out to the flightdeck with a couple of our .45's. Not a single jam in over 500 rounds. Those magazines are probably still feeding reliably today.
In 20 years of loaded condition there was no discernable problem with any of the magazines that were in that case. "Spring Set" is a myth best left in the dust.
"The sword that cuts down evil is the sword that gives life"
*10 Ring, MBR and Reloading Clubs: #436*