Originally Posted by
Ex Pres
You are correct that there is only one C9 [cassette] spacing, but the rear derailleurs/Ergo shifter used two different actuation/cable-pulls to get there. If you stick with Record and Chorus Ergo/RD it's easy - all 9s is old pull, all 10s is new pull. In the other groups it's not always so easy.
Not true,
In 2001 they were still making 9s Record and Chorus along with the new 10s. The 9s platform in 2001 used the same derailleur as 10s (except for markings), so it needed a different cam (the inside part of the ergo lever that controls the indexing)
There are therefore 2 9s cams. The original which was marked with a 9 in a circle, and the one with the right spacing for the new derailleur, which was marked with a 1 in a circle (1 stood for 2001, or 9s in 2001, vs. old 9s).
They never made new cams for 8s to work with the new derailleurs because by 2001, they considered 8s obsolete.