Continue reading...Hi-Lows-Note via Northlight Images has uncovered a patent for an RF mount macro lens. The optical formula is for an RF 90mm f/2.8L IS Macro. Northlight points out that the image stabilization group (L12) is further forward than the normal positioning for IS groups.
Japanese Patent Application No. 2017-108266 shows two different optical formulas.
Specification and lens arrangement of embodiment 3