Originally Posted by
miamijim
It the real deal and it's old. I don't think anyone can tell you the exact year.
Colnago went through many incremental changes to their frames which are helpful with estimating the age.
Holes in the Bottom Bracket vs cutouts.
Above or below bottom bracket cable routing.
Water Bottle Cage Braze-ons
Shifter braze-ons
etc.
So, assuming the list posted by
Sir_Name is accurate, then one should be able to narrow it down to within a couple of years (assuming the frame wasn't modified later).