I've been reloading for just shy of 30 years. Properly stored I've never seen powder go bad. It is pretty stable stuff.

Rifle powders are usually "log", especially the older stuff out there. Shotgun usually "flake". Pistol usually "ball". Many shotgun powders double as handgun powders like Blue Dot, Red Dot, Unique, and others. There are exceptions to everthing above.

There should be a lot number on the cans. There should never be a combination of log, flake, and or ball powder in any single can. If you see this, dispose as directed above.

Have fun, always start out low on the weights, check the tare weight on the reloading scale every time. be safe.