I have Alcan powder bought in the 70's when a store sold discontinued powders. They were old then older now and still good 40+ years.
A keg of Dupont 4895 purchased in 1987 went bad long before I could shoot it up, while I still was using Mil. Surp. 4831 made in WWII.
I pulled down some WWII era 8MM ammo in 1990 to get the bullets because it would not fire, the powder had degraded and corroded the case and bullet bases.
It all depends on the QUALITY and CARE in manufacturing and the amount and type of preservatives.
Storage counts and cool is better, but all of the above powders were stored together after I bought them.
I do not know how to determine which current powders are going to last. Does anyone have an idea?