That's exactly what I would love to find!
I would also be happy to find a piece with the J.I. Co label that is documented in a book or other reliable source as being by one of the famous makers (so maybe you have such evidence?). Or the other way 'round, like with the seahorse. It's in the J.I. catalog, so if had a Barbini/Cenedese or other label, I would be pretty satisfied. But like you said, a piece with a maker label AND a J.I. label would be the ultimate. :-)