Son #1's godfather was a meat cutter for one of our largest supermarkets. He told me once that when a piece of meat goes past the sell by date, they will often bring it back inside, turn the piece of meat over and rewrap it with a new sell by date. As the piece of meat sits in the styrofoam tray, the blood seeps to the bottom and the piece of meat turns grey looking on top. Because the blood has gone to the other side, it looks freshly cut. But the second sell by date is much shorter than the first one was. Often only for a day. Then it gets that reduced sticker on it. Since meats I buy go into the freezer when they arrive home, I have no problem buying reduced meats. I take them out of their packaging and rewrap them for the freezer.
BTW, don't ever buy cut up stew meat in the styrofoam packing. The inflated price is labor cost. All it is, is the trimmings from all sorts of cuts. Buy a good chuck meat and cut it into cubes yourself. That way you know what you are getting and at a cheaper price.