I know blackpowder lasts forever, it doesn'e absorb moisture like the substitutes and even after getting wet if it's dried out it still performs fine. I read an article somewhere from Knight Rifles that said Pyrodex once opened should be tossed after a year? I have a can of Pyrodex that I have had for years, probably 10+ and it still seems to perform fine, nothig erratic. I think if you keep your powders in a dry temperature stable environment (if you can put the subs in a place with dessicant all the better) you should't have any problems for a few years at least. That said I know some subs like Clear Shot, in my opinion, go bad quickly. I have BP, Pyrodex, 777, and some Shockey's. Like I said the BP I have had a long time, same with the Pyrodex, the 777 only a few years but seems just fine still and the Shockey's I just got a year ago to try out.
Pyrodex does fine if you keep it dry. Unopened, I bet it lasts lots longer than we manage to keep it without shooting it up. I got 8 pounds from a friend's estate about 10 years ago, and it was old then. Don't know about the date of make, but the price tag is $9.29- and those are "Alaska" prices. Jugs are just fine when opened, though I use them up in 2 or 3 months after opening.
American Pioneer is BAD for deteriorating after you open a jug. A friend chronoed his after 6 months and was getting about 25% less velocity than when he first opened the jug.
Not enough experience with 777 to know, but it appears really stable.
I've used Pyrodex pellets, but gave them up as a very bad investment in our damp climate. Worked fine out of a new box, but withing a couple of months I started getting misfires with #11 caps. By six months, I'd have to pop 4 or 5 caps to finally get them to light off, and even them some of the reports sounded kinda weird. I'd say use them up right away or throw them away. I surely wouldn't start a new hunting season with last year's pellets, even with #209 caps.
I've got a number of cans of real black from the same estate where I got the Pyro ten years ago. The coded dates on the cans run all the way back to 1973 and the prices down to just under $3! And some of the cans were partials. Even from the partials, the 35-year old real black works just as well today as the new cans I bought last summer, even after spending allthose years opened in a wet climate. That's saying something!
I have had a can of 777 that was opened sitting in my safe fro about 2 or 3 years now and at the range a week ago worked fine with #11's. I also have a de-humidifier gel in my safe- may have something to do with it. Then again, there was a speedloader loaded for my .50 since last moose season that I fired off at the range the same day and worked fine in my 209 gun- it had been stored in the center console of my truck (OOPS!!!).