I'v some german 9mm marked 1917 and various 8mm from the 60s and greek 303 boxer primed from the 70sIf the storage was dry, it'd be a lot longer than 25 years. Although "average temperature" can be a tricky thing. If it was stored at a temp of 150°F for 6 months, then at 0°F for 6 months, that's an average of 75°, which might be a bit more deleterious than a constant temp of 75°.
In the late 70's and early 80's my regiment used ammo in our retired BREN guns that came in cases marked "NOT FOR USE IN SYNCRONIZED MACHINEGUNS AFTER 1927", IIRC the headstamp was from 1917.
And the manufacturers replied "there is nothing that can be done to make a primer go bad in 10 years that won't make it go bad in 10 minutes". Never gonna happenWasn't there some politicians that wanted to make it law that primers had to "degrade" over time so ammo would be bad after like 10 years or something?