They have a shelf life of supposedly a least a few months although I think it is over a year. Taco Bell does not refrigerate because of the expense plus they will use them up way before then. As long as they cycle their inventory (use the oldest box first), they will be okay.
Hmmmm, wow! that's interesting. I have not really thought about that before! My family refrigerates them, maybe my mom heard it was good or something. Wow, never really thought about that before!!!!