According to this page, you can distinguish between a Super and a Mexico based on some crimps
- the Colnago Super can be identified from one crimp either side and center on the top tube, one either side and center on the down tube, and inside the chain stays
- a Colnago Nuovo Mexico has two crimps either side and center on the top tube, 2 crimps off center either side of the down tube (so dt has 4 crimps in total!) , and none inside the chain stays.
At least it seem that it can be said that the bike is pre-1985, because according to the same site "later than 83/84 Colnago had rounded seat stay caps, instead of the stamped ones" like yours.
Have a careful look at the site I mentioned above: there are two very similar bikes, both painted with identical blue color but one is a Super and the other is a Mexico.
It should help identifying your bicycle. Good luck and please come back with your findings!
You may have a look at this site,
where a lot of useful information and pictures of Colnago of various years are published.
I still think yours can be a Mexico, although this site says that the spool-shaped bridge between chainstays is usually found on the Super.