As someone who works in the costco meat department, I honestly don't know the answer to your question BUT for what it's worth, costco raises their own chicken and ever since the shortages on meat started, we've had to bring in chicken from other suppliers just to keep up with demand.

Costco chicken breasts has 9 vacuum sealed packages in a single box whereas the other brand just has a bunch of chicken breasts in a bag in a box. We have to put this chicken in styrofoam trays and wrap it and whenever we do, it really grosses me out how there's dozens of breasts just sitting in the big bag of chicken brine. And even after letting it drain out, the trays will still get full of chicken brine and leak all over the place after sitting for a few hours. I genuinely don't understand how that much fluid can sit in just a few chicken breasts but always buy Kirkland brand whenever you can.

When it comes to meats, costco brand is gona be the best quality for the best price