After I made my last post I sought out the legacy information on the Pro SD from the Mamiya/Leaf site. This is what it says about screens:
Vertical Split Image
Same as Matte, but with a vertical central split-image rangefinder wedge added. Matte surface can be used for focusing, but the vertical split-image feature makes focusing easier and more accurate for subjects such as portraits.
Cat. # 214-527
All matte with Fresnel lens, suited for general purpose photography. (Supplied with camera)
Cat. # 214-520
Same as Matte, but with perpendicular grid. Pattern ideal as a compositional aid. Grid intersections also useful as reference points for multiple exposures.
Cat. # 214-521
Same as Matte, but with central microprism spot added. Provides an alternative Rangefinder Spot screen with same benefit of enhanced focusing precision.
Cat. # 214-523
All matte screen with small aerial (totally transparent) spot with cross hairs. Used for parallax focusing and designed for special high magnification applications. Especially suited for macro and telephoto photography.
Cat. # 214-524
Same as Matte, but with a 45° split-image rangefinder wedge surrounded by a microprism collar. Highly versatile 3-way focusing (rangefinder, microprism, and matte). Ideal for general purpose photography.
Cat. # 214-525