As of right now the UPC is tied to the site through backend code, so it is "there" its just not actually visible. This makes it challenging for customers to verify actual item that shares similar imagery to another item. Supplier part code is visible, but consumers are much more likely to know the UPC than they are to know the supplier part code.
I'd like to recommend surfacing the UPC right next to where we surface supplier part code on the product profiles.