Reader Leo writes in with some helpful information that will allow you to avoid stale candy:
I work at a small-volume store in the midwest, and the other day my supervisor asked us to check all of the candy in the checkout lanes to see if it had expired. M&M Mars and Hershey brand candy both had different, indecipherable codes on the back which tell the expiration date. After calling the 1-800 number and finding out what the codes meant, we discovered that most of our candy stock was expired by a year or more. We even found candy that went bad from 2004. I figured I should share the codes, so people won’t buy expired candy, because it’s out there.