Dry-aged beef has spoiled. The trick to it is that you need a fairly large piece, like a whole leg or side, and then you trim off all the bad stuff on the outside. More simply, they don’t butcher it then age it. If you go buy a piece of dry-aged beef it’s gunna act a lot like any other piece of meat but if it hadn’t been butchered you could just keep aging it beyond when this individual piece would have gone bad.