Sorry - just a quick straw poll of whether or not you would cook/eat some lamb that you have meant to casserole every night this week (!) and haven't yet found the time for and which is now out of date by one day...??!
What difference does a day make? It looks a little discoloured but not gooey/yucky - haven't yet opened pack to sniff it. Would you cook it well and eat it anyway?!
(Seriously don't do vomit, so always worry about things like this - probably unnecessarily!)