Understood. Springs don't fatigue under constant pressure. They fatigue from use - compress, stretch, compress, stretch. And it takes a lot of that to wear out a spring.

Most of the mags I have that aren't loaded (thus far) are that way because they are backups - still in their original packaging, unopened. I always keep a minimum of three active (and numbered) mags per firearm, sometimes more. Anything above that I consider backups, and those may remain in their original packaging. Or at least in the past they have remained in their original packaging...