I used to get mine at Costco too, because they were Rayovac, not sure what’s going on there now. I’ve been getting Duracell 312’s at https://www.localbattery.com for the last few years and very happy with them.
I’ve stopped buying things at Amazon that are easily subbed with fake or old product, so even Duracell could end up being old or relabeled. All my regular batteries (9v AA, AAA, etc) are Duracell from Costco now…