So Rh- actually means Rh-D negative. And Rh_null_ should really be Rhesus negative (or true Rh-, but that term has a too engrained “slang” meaning to be used)
Fascinating. I knew about J and K type bloods. I didn’t really give any thought to – actually I suppose I just didn’t understand that Rh is really a set of antigens just like O/A/B/AB are antigens.
More research is required for my brain.