Graflex RB shutter speed plate variations

In scouring online sources for yet another Graflex RB, I notice there are some variations in the shutter speed plates. Some list 6 Tension Numbers from 1-6. Others just have the two options of "Low" and "High". Some list Curtain Apertures from A thru D, others in fractions of 1/8 thru 1 1/2.

I've read through manuals, and trawled Graflex.org, but can't seem to discover if one version is older than the others? Does anyone know the historical progression of the variations? Or perhaps one version was targeted more at professionals? Any help appreciated...

6 speeds, 1947-or-so on. 24 speeds, up to 1947.

Tension settings 1 -6 from introduction through 1946/47, Lo -High from 1947 until end of production. Super D of 1945/1946 had the six step tension but labeled Lo at lowest position and High at the highest setting with no markings for the positions in between and 6 speeds in the table.

Perfect... thanks folks.