I think I’ve mainly just used the bolded part (seems the boldface must have some meaning, right?). And it makes sense: in a UPC code, the final digit is a check digit, and the leading digits identify the company. So if I’m counting right in ListMyCDs.com’s example, they’ve boldfaced the product code and one digit of the manufacturer code (probably EMI has more than one).
And of course the full code is already present in the barcode field.
But I guess it’d be nice if someone actually had access to a printed catalog, and checked.