I've also acquired some WW/Korean vintage magazines which functioned normally after having presumably been left loaded for all those years. Didn't say it couldn't happen.
Neither did the Colt instructor. Neither did any of the other manufacturer reps, engineers, repair technicians, armorer instructors or a spring manufacturer I've queried on this subject.
On the other hand, none of those folks would guarantee an inexpensive spring's continued ability to provide intended normal service beyond reasonable (and presumably cautiously conservative) limits, with the implication that being left fully compressed for an extended number of years would contribute to the lessening of the spring's ability to exert desired tension at some point. Where that point may be is what's open to much debate and conjecture, and no small amount of variable anecdotal experience.
Then again, I've seen others of similar vintage which didn't offer such wonderful reliability after having been left loaded, too. Listened to a lot of other folks in the field offer similar examples, too.
But this is a bit off the subject of modern magazine springs and their useful service life under different circumstances, such as being left fully loaded for long periods of time.
Glad to her your G23 magazines are still working for your needs.
FWIW, though, I've personally observed Glock magazines exhibit weakened magazine springs in various models/caliber across a range of different time periods, and with guns which were being carried by folks who claimed they didn't shoot them often. Some have been as soon as 3-4 years, and some as long as a reported 10 years.
The armorer instructors generally make it simpler for their target audience. You want to make sure your people's guns are going to function as well as can be expected? Change the springs as recommended, or as may be required based upon observing any functioning issues that may occur (regardless of how soon that may occur, if it does appear to be spring-related). Personally, I'd rather not wait until the first spring-related issue arises, since there's no way to know when the first
functional indication of a weakened magazine spring may occur - on the range or somewhere else.
Now, who knows what would be told to commercial customers if they call back and ask the customer service folks such questions? Sometimes I've called 'cold', without identifying myself as an armorer and asked customer service folks such questions and got the same answer as I did in an armorer class. Sometimes I've been given a different answer than I heard in the armorer class, too. Other times I've been told they didn't know and I was transferred to a technician for an answer.
Myself? I've pretty much decided that I'll err on the conservative side of things when it comes to spring replacement in guns dedicated to defensive use - (compared to range enjoyment use) - both for my personally-owned guns and those of other folks for whom I'm responsible for maintaining their guns.
I certainly don't claim to have the definitive answer, and have heard so much from an entire range of folks who ought to have much more experience and knowledge in such things than me ... that I've just decided to take the path of least resistance and replace things like springs either as often as recommended by a manufacturer, or even sooner.
The last thing I want to happen is for a magazine (or recoil) spring in one of
my guns, or in an issued gun for which I share responsibility for maintenance, to weaken and fail to provide for normal functioning ... and then have someone come behind me (if it's my gun) and explain how a spring was worn and too weakened for its intended function, or, if it's another cop's gun, explain to the family why I wanted to wring some extra service use out of a spring which hadn't yet exhibited a failure on the firing line.
FWIW, I'd prefer to replace a spring
before it exhibits a failure related to weakening, since there's no way to predict when and where that first spring-related 'functional failure' may occur ... on a range's firing line or out in the street. Admittedly, some failures may occur without warning ... out-of-spec/defective part, unintentional damage caused by the user, etc. ... but aside from those hopefully infrequently occurring unpredictable instances, I just prefer to replace these types of spring before a functioning issue ever occurs.
Not being a licensed gunsmith, nor employed by any of the firearms manufacturers, nor be anything even remotely resembling any sort of an 'expert' at anything, nor responsible for anyone's guns other than my own or those of my agency, I would generally suggest that someone who has such a question call the manufacturer of their particular firearm and/or magazine and ask the company what they recommend. That would be a good place to start.
Springs are relatively inexpensive, all things considered (and especially when considered against the cost of buying ammunition at the present), and most owners don't shoot anywhere nearly as much as the folks who have an interest in firearms sufficient to allow them to discover that these firearms forums even exist.
I'd still like to see all of the older, little-used (infrequently fired) pistols brought through our CCW range exhibit normal functioning when it comes to their magazines/magazine springs every time, too. (Okay, might as well wish for all the other maintenance & ammunition related issues suddenly no longer occurring.
) Hasn't happened over the course of several years, though, and I'm not holding my breath.