I can tell you that the M80 v3 woofer is marked on second "ring" in as YD166-19. The HP woofers that I can examine in the M100 have no "part number" showing, but the rubber "ring" looks wider. Can someone with non-HP M80 v4 speakers see if it has that same YD166-19 part number?

I have a new M80 v4 and I can't see any writing on the speakers other than the Axiom around the front bezel. I don't know if you were talking about something on the back of the speaker driver.

I am pretty sure they are the same, the only ones that got updated where the HP 6.5 Woofers.

All V4 have cast baskets.