Eggs, for example, can be consumed three to five weeks after purchase, even though the “use by” date is much earlier. A box of mac-and-cheese stamped with a “use by” date of March 2013 can still be enjoyed on March 2014, most likely with no noticeable changes in quality.
My confusion is with the flash pasteurized milk. The expiration date is so far ahead in the future. But once you open it you only have about 7 days to use it – according to the side of the box.