I wrote to Muhle direct. My understanding is all Rocca heads now have a CNC machined 316L stainless steel top cap and CNC machined 316L stainless steel base plate. The top section of Rocca handles are also CNC machined 316L stainless steel, that are press fitted onto a brass middle section (this may be different for the all stainless steel handled version, announced Nov'19).
Updating previous posts and also observations by
@Dr Watson, I would say the difference between each version of the Rocca head, appears to be as follows:
V1 = MIM top cap and base plate.
V2 = MIM top cap and MIM base plate (MIM circle marks polished off the underside of the top cap) blade posts and centre post are glued / welded/? onto the top cap rather than a complete MIM mould, as V1.
V3 = MIM top cap (complete mould with visible circle marks on underside of top cap; no glued / welded centre post or blade posts) with CNC machined 316L stainless steel base plate.
V4 = CNC machined 316L stainless steel top cap and base plate (I am assuming "CNC machined top cap" means this includes the centre post and blade posts in the machining; but I do wonder if my assumption is correct after the surprise at how V2 heads were manufactured.
I am not sure how you would differentiate between a V2 and V4 Rocca head; perhaps someone who works with metals would immediately know. I think I may have a V4 but it looks identical to a V2. In any event the manufacturing tolerances on my latest Rocca are visibly tighter than my V3 Rocca.