Many years ago, my aunt asked Dad(her little brother) to sell a pistol for her- surprised him, he had no idea she owned it. Anyhoo, she said she'd gotten it ~1940, had fired one "clip" full through it, did a rudimentary cleaning on it, reloaded it, wrapped it in an oily rag, and never fired it again. It was kind of a strange looking thing, maybe a Savage? It shot .32 ACP, had a full "clip", and about 2 dozen loose rounds in an old snap-shut cloth coin purse.
We went to the dump with it, just Dad & me- I was probably just turned 10 yrs old, call it summer of '63. He removed the magazine, tapped the rear lightly against the heel of his hand, put it back in, racked the slide to fill the ~22 yr empty chamber- and fired one shot into a coffee can about 10 yards away. He then proceeded to empty it, one-handed, *fast*, into the same coffee can, missing only once.(He'd served as an MP in '46-'47, was well trained on the old .45 auto, and even though he didn't own a pistol often outshot folks with their own short guns.)
That magazine had been loaded for 22-23 yrs, and didn't bobble once. We shot up the rest of the ammo- I say we, I got to shoot it twice- and a couple of days later he sold it, think it was the local constable who bought it.
So, in general, I've held the opinion that if a magazine has a decent spring, it can be left loaded for years- even decades- and still feed 'em fast. FWIW, one of my Xxxxx magazines has been loaded full for over 5 years now- & no, I don't worry about it a bit. Besides, those Xxxxx springs are *way* too strong!