Just bought two cans of IMR4350 from an old guy getting out of target shooting who kept meticulous records. The cans were marked with the date he bought them and still sealed, 1970, 34 years ago, and shoot just like new 4350.

If keep dry and well sealed it will last a very.! long time
i still use my GRAY B Powder i bought it at the trap club
in 1969. i use it in 38's and in some 357 load's
i also still us my Herter's 209 trap powder..

Open the cans and take a whiff. If they smell like solvent, then as a general rule of thumb, they are still good. I have used powder that was stored in a cool, dry place for 10 years and it was still good.