As an aside.........beef used to be hung for 2 weeks before it was put up for sale. The point was that the bugs would help tenderise the meat. Chances are that that beef is well under 2 weeks old so go ahead and eat it.
Our local news station ran a expose' on local grocery stores who were repackaging their meat after the sell by date expired. every one of the major chains except Albertsons did it. Pretty scary stuff