Technically, there is some shelf life for some black powder. Back in the mid 1980's some experiments were done with different ages and brands of black powder. Nearly all powder manufacturers boil the water used in the process. In days of yore, water was boiled in copper vessels. As a result trace amounts of copper were carried over into the finished powder. With the trace copper, bacteria could not grow on the black powder. For a very briedf time in the 1980's one or two brand of powder were made using water sterilized water that did not possess that trace copper. Asw a result the same type of bacteria that live in under ground coal could start to grow in the powder and cause a chemical breakdown of the powder. As soon as that was discovered, the problem was cured. For that bacteria to grow, the powder needs to be exposed to (1) moisture as well as (2) the bacteria and (3) it must be a powder that doesn't contain a bacteriacide like the trace copper. So, chances of running into a powder that could break down are very slim and nearly null if you keep your powder out of mines and sealed from moisture.
All that being said. I purchased a few hundred old remington 43 Spanish black powder load cartridges from the 1880's. Broke some cases down and kept the powder (about 300 grains) in an open container in a somewhat damp basement for three years and it went off no problem.