The rub marking below the frog stud could certainly be from a frog... although I don't know if it could be attributed to a specific variant. Rub markings tend to be on the sides of the scabbard (where the frog may be the tightest) running parallel to it. Over time, abrasives like dirt, sand, etc. often collect between the scabbard and inside of the frog, which increases wear. In addition, the bottom edge of the frog pouch (both sides) will create a somewhat straight line on the back side of the scabbard and a arced one on the front side, which is the demarcation point of maximum travel of the scabbard while riding in the frog. Lastly, the "tropical" web frog was initially for use in a Mediterranean environment. German forces in North Afrika likely initiated more widespread usage of this frog. As the war continued and leather became a scarcer commodity, webbing was used on a much wider scale to compensate. This also prompted experimentation with other ersatz materials like "Prestoff" (laminated paper & leather), rubber-impregnated webbing, etc.