Only if it has white mold growing on it... LOL
Seriously, I can't see any reason it would truly go "bad" if it was packed away in a dry place. I'm gonna guess that a lot of the boxed/mined/natural ferts we see on the shelves were mined months/years before they were packaged and repackaged and resold...
probably only one way to find out. Brew some up!
At the very least it would still make a great soil amendment.
good luck
s h