Turns out all this means is that when the buy stations close in final circle, the buffer zone also disappears, so ammo caches/munis won't work even 1 inch into the gas.
Previously you could use munis or ammo caches if you were within 40m of the final zone. That's it.
"Disabled" is a little ambigious but assuming the worst, all loot in the gas will despawn at the start of final circle (so it's the end of firesale stim stacking).
I assume ammo depots near the final zone will be force-closed just like buy stations.
Will have to test fully.