This bike is an example of why you can't attribute neat, year-end changes to frame details - it doesn't fit the timeline. It's a 'tweener. The absence of "Colnago" in the caps should indicate late 70's according to the timeline, but the block bridge says circa 1980 or later. Lots of these bikes that don't neatly fit the timeline exist - it's easy enough in this case to say 1979-80 and be pretty much on the money, given the coexistence of two details that should be chronologically separated (according to one theory, anyway).