Consumer Reports had a recent side bar about this and explains the difference between 'sell-by', 'use-by', and 'pull-by' and and other confusing messages. It recommends a standard date stamp that can serve the buying public - as opposed to what will protect retailers.

...just as the expiry date of eye-drops told by pharmacists -- "till the printed date if unopened but to be used within 1 month once opened"....it would be much better if printed on product or package insert