Kirkland isn't a relabel. Kirkland is a house brand, and they specify the product, and contract a company to produce it. Sometimes, the spec is "make same thing you already make, put it in Kirkland packaging". Other times, the specifications result in a different and unique product. Amazon does this with their Amazon Basics and there are probably other house brands, too.

That doesn't necessarily mean it's exactly the same products. Costco can request changes to turn the product into something they are happy to put their label on.