To add more confusion to the issue, take a look at bulgier's list of scans and check out Bikecology-1981, pages 6 and 7. This shows details of U.S. import Colnago bikes and framesets for 1981. There is no crimped tubing on either model. Shifter cable routing is over the top of the bottom bracket, and forks for both models are the flat crown type. Also, chain stays have the "chrome" decal rather than the full chroming as shown in the catalog. The Bikecology ad indicates that the only difference between the Super and Mexico models is tubing weight. I have an assortment of Supers and Mexicos and a very accurate digital scale and have detected no difference in weights for bare frames. So I think even this information is suspect. Ray, perhaps you could ad these scans to your analysis.
I think the Catalog is a late 1981, and that the Nuovo Mexico depicted is more of a preview of the 1982 model. I believe the Nuovo Mexico was used by Colnago as the styling innovator; the first to use crimped tubing, sloping crown fork, under the bb cable routing, stamped chain stays, and braze-on front derailleur.
I also think there was a difference between european market Colnagos and some of the U.S. market frames. The euro bikes tend to have more chrome, either lugs and/or stays. I don't know why. I think Steven Maasland has some theories.
Jeff Pyzyk
Milwaukee, WI