First of all, can you add a photo of the top of the top tube including both lugs, as well as the top of the downtube lug.
Do you see any clovers in lug cutouts our "Colnago" script anywhere on the bike?
I've learned never to say never with Colnago. But, I'm not convinced that is actually a Colnago. If it is a Colnago, it wouldn't be a top of the line offering from them. However, it does have some features of at least a fairly good frame.
For dating the frame, the semi-vertical short dropouts were only used for a couple of years and should be able to give you a very close date.