OK Dave, now I see what you have. I concur, I can not see how that would work in the normal direction. I don't have an early style to take apart at home, so here is what that part should look like. As you can see in the drawing from the Simplex 125 manual, dated 1953, in the obsolete parts section, the cut is the opposite direction.
Call Wayne this morning and see if he has one, and have him take a picture of it.
Now to the detective work. As KartJockey has the same situation, I wonder if Simplex just simply ran out of the throttle side tubes, and occasionally substituted a left side to keep production rolling? Are they interchangeable? Does anyone else out there have this situation?