I still have a lot of leftover Vallejo inventory from about 12 years ago. It's not responsible to sell it, but I've been using for my own stuff all along, especially since I got the iModel kit app years ago to mix anything from on hand colors.
These are both MA and MC, have been sitting stored in a crawl space (and on my bench) in the attic in NY, so hot and humid to frigid dry. Even paints that have been opened still work perfectly, I thin everything about 50% anyway.
The only problem I've ever had is that I use those cheap empty eyedropper bottles to mix and store AB thinned colors (with a stainless BB to help mix) and some of them have the inside caps too long and when you tighten the outer cap, they'll eventually crack the lid and dry out. Bt all that reain intact are fine, just need a good shake.
I find water based paints evaporate more slowly than others (yes, they dry faster, but that's oils used in other types). Solvents are more volatile, that's why your bottle of Tamiya Extra thin will disappear if you leave the cap off, but the glass of water on the bench will stick around.
I have acrylic artist paints that are over 40 years old that still work fine.