Signs of deterioration would be a foul smell when you take a whiff of it (don't jam your nose to close at first....we don't want you to bounce your head off the floor!!!) and when you open it up, when you pour it, if some of it comes out in a fine cloud like baby powder (a fine cloud of black dust) that's an indication of bad powder. So, for the twenty some bucks a pound....why risk it? But, if it smells and looks fine....I would use it with no apprehension.
MHO
Dave