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Old powders: Old Dupont IMR rifle powders, I have read, will decrease in potency with age and/or storage in above-80-degree temperatures. My personal experience tends to bear this out, in that some 1968-vintage .243 loads shoot about 2" lower than newer stuff. I've never noticed any pressure signs on 20-30 year old '06 stuff I've plinked away just to have an excuse to reload...
Don't know about modern pistol powders. I have some GI .45 ACP, EC '43, which still shoots about the same as it did in the 1970s-80s...(I found some 1921 vintage .45 ACP a couple of years back which had dead primers...)
FWIW, Art
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