The Original Dry Bag Steak | Make Artisan Dry Age Steak at Home › Forums › Dry Aging Steak › Dry Aging Steak with UMAi Dry® › Newb: Rib roast from supermarket. Not cryovac packed. › Newb: Rib roast from supermarket. Not cryovac packed.
Sounds like you may have lucked out this time. Problem with supermarket display case beef is you have no idea how long it has been in there, how it was handled and even more importantly it is sometimes blade tenderized. That tenderization is common practice at COSTCO. What that means is any surface bacteria has thereby been driven into the meat. While eating that meat soon after purchase doesn’t cause a problem BUT dry aging a blade tenderized piece is asking for trouble.
Now about your meat – if you do have surface bacteria it will stay there and you’ll be trimming off the hard exterior anyway so I’d say you are fine. Just let your nose continue to be your guide!