What is the shelf life/expiration of chews - opened and unopened?

Our pet chews will always contain a "best if used by" date based on the time it was manufactured.   They are completely shelf-stable, so they do not need to be refrigerated. (Certainly, if someone wants to refrigerate them, they can, but they will stay soft and fresh as-is.) As long as you keep the chews zipped up, they will be fine through their expiration date.  However, they may dry out/harden if they aren't zipped up.