As TimmyMac says, the newest K/L lenses are equivalent to the first RZ lenses, but most of the RZ lenses have been refreshed since then. 110/2.8 and the 50/4.5 ULD are not available for RB because (I think) they have a too-large exit pupil. The film/flange distance is shorter for RZ than RB (less retrofocus required for wideangles), and the RZ camera throat is larger (larger exit pupils possible, e.g. for the ULD, 75-shift and 110).