Forge markings on Uppers?

[Robb Jensen]

Any chance on getting another list showing the manufacturers and where they get there uppers?

Case in point, my m&p15A has a keyhole mark on the right side of the upper, and so does my friend's bushy varminter.

Maybe there's endless possibilities, but I've come up empty handed on googling this subject, and the knowledge base of M4C is quite incredible. Thanks in advance.

Those are both Cerro forgings (unknown who does Bushmasters or S&Ws finish machining).