Originally Posted by
Dan333SP
He's just trying to figure out a compatibility chart for mix 'n match groups. That can be important if he buys the current Tiagra levers and finds out that they can't shift a 6600 RD correctly even though they're both 10 speed parts, ect.
I guess I understood that. I think the best bet is to just assume incompatibility except in the very few well publicized cases of known compatibility. Examples are the 8-speed Shimano RDs and 9-speed levers and the SRAM 10-speed RD with 11-speed levers.