I have never been afraid of old powders. I had some IMR powder from the early 60's. Had been stored in the opened, original cardboard container (probably 15 pounds) in the garage in East Texas. Was using it to load for my deer rifle up to last year. Every thing was fine.
Went to dig some out for a friend today, and it had some reddish color in the air in the container, and smelled real strong of acid or Clorox. Dumped it in the yard. (Sure hope my neighbor don't toss no 'butts over). Seems like when it starts to go, it goes real quick. But there was no doubt it was bad.
Went to looking, and another old 1 pound can of IMR had rusted through the metal can.
Don't think it's worth taking the chance on keeping the old stuff any more. Might start a fire where I don't want one.