The "designated" triple just has a wider range of cable pull on the L shifter. I've seen both the 8-sp and 9-sp 105 L STI shifter used on triples, but have not done so myself. The 9-sp came with with yellow lettering outlined in blue, and with black lettering. I was told once that all 9-sp 105 L STI's will handle both 2/3 speeds. I sure don't know. There has to be some triple 105 STI's made in both 1055, 1056, and the 5500, because I've seen plenty of 1055, 1056, and 5500 triple cranksets.
Friends don't let friends drink and wrench.
1985 Raleigh Competition
Racing USA Series-Coleman made me do it.....
1987 Bridgestone Radac
- Aluminum (sadly, the frame is toast, RD hanger snapped off)
1988 Centurion Dave Scott Ironman Master
1989 Centurion Carbon-R
- Carbon Fiber