I think the subs are more susceptable to age deterioration, especially if they are exposed to moisture or changes in environment. I suspect if kept sealed in cool even temperature they will last quite long also but probably not as long as real black powder which is as stated capable of remaining close to original decades later. I have read reports of Pyrodex and Tripple Seven losing some power over time but personally I have not seen that although my conditions are quite dry and temperature stable (Arizona and stored in air conditioned buildings).