As I stated previously, frame part details like that one have more to do with the specific era of the bike than with the model, as different Colnagos throughout the model range would have shared the same BB shell. It's the tubing that's the indicator in this case, and no other Colnago had the channeled tubing aside from the Nuovo Mexico and Profil, AFAIK, and that's not the Profil fork. It would be interesting to find other Colnagos with that shell, though, as it might help pinpoint the year.