According to info published in Hatcher's Notebook smokeless powder will deteriorate over time. If Black Powder is not exposed to moisture it seems to last forever. Early non-corrosive primers did not have a real long shelf life which is why the Army stayed with the corrosive ones at least throughout WWII. By that point improvements were being made & shortly after that the switch was made, don't recall the exact date offhand.
Fortunately when smokeless does deteriorate it grows weaker, not stronger so the only real danger involved is the possibility of a stuck load, normally a wad in the case of a shotshell.
When firing old load always be aware of this possibility & definitely check the bore if any sounds the least bit abnormal. "SO EASY" to do on a double.
