If anyone doesn't believe me, load a mag and leave it the fully loaded state for a couple of months, then compare it to one that you'd fully loaded last week.
I just checked my mags. And it took me a while to accomplish because I had over forty magazines to download and take apart.
All, as in every single one, of my long term 'compressed' magazine springs are just as strong as the brand new springs that I have in my gear locker. These spring haven't been compressed for just weeks or months...every spring came out of mags that I had loaded and stored in an ammo can while I lived in San Diego...which was over twelve years ago.