What really constitutes “proper storage?” I had a whole bunch of cheap Remington .22 stuff that I had in the back of my closet for ca. 20 years. Went to shoot it, and only about 25% worked. Most of the stuff had turned a bit green.

I now keep my ammo in a chemically dried space.

Was it just the cheap stuff, or should ammo in general be maintained in an environment with mechanically/chemically reduced humidity?

A cool dry place would be just fine.

It's the storage container. You know why those ammo cans have that lever lock feature, and that rubber gasket around the rim? To keep moisture out, no matter what. That green color meant your ammo was stored in conditions where moisture could get to it on a continuous basis, and when that happens brass WILL corrode. No moisture, no corrosion. That's why ammo made in the 1960's in places like Turkey and Romania and stored in soldered shut in tuna fish cans is still very shootable today.

Just saw this thread. I've tried reloaded ammo from 20+ years back and it didn't shoot very accurately. At 100yards the group was like 1 foot!
I'm guessing that moisture got in and tainted some of the powder but the rounds looked fine from the outside (no corrosion,etc.).
All the rounds fired but the accuracy was....terrible.

I store 300 rds in quart zip lock bags and then put the bags in the 3 gallon tubs. Each bag is marked with the date and load data.

I've got about 25,000 rds stacked up this way. Most gets shot over about a two year period, but I don't like changing my setup so I'll load a few thousand of 40 then switch to 45 then 38super, ect, ect so it's about 18-24 months to make the full cycle through all the cals.