Lump charcoal can last just about forever as long as you keep it dry.
Briquette is another story. It is made of binder such as starch and absorbs moisture much easier than lump charcoal. Self-igniting charcoal has a year or two shelf life before the igniting chemicals evaporate.
What should you do if your charcoal goes damp? For either lump or briquette, you can lay them out in the sun for a day. But if the briquettes easily crumble, you may as well get a new bag.
