In my experience all the Colnagos have 2 cable guides and not three.
If memory serves, the only visual difference between a Super and a Mexico was the "mexico" label on the chainstay. I have a BikeCology ad showi ng the two, from '78, I'll dig it out and post it.
When I see a Colnago with 3 cable guides, I figure additional forces were a t work there.
Palo Alto CA USA