Also only anecdotal evidence --
In my small police department, most of the issued magazine springs were good for years, but a few of them went soft.
In my personal stock, most of my magazine springs, for several different pistols, have been good for decades, but a few of them have failed.
My observation has been that a weak spring that won't feed also won't lift the slide stop, so that's been my quick test. If the magazine will still lock open the slide, it will still feed too.
Carry magazines and ammunition should be checked regularly - monthly - in any case, for gunk, corrosion ... or weak springs ... that might not be apparent externally.
On that tangent, I've seen guys rotate cartridges from the chamber back to the magazine with the intent to spread out the damage - if any - from loading and unloading. Seems to me that you'll just end up with a whole magazine of bad ammunition.
Other than an initial inspection check, ammunition in my magazines stayed in my magazines. I would use one cartridge for the chamber for a month, then put that one into the practice pile, and start again with a new round.