Let's look at the guide:

Headlugs:
1973: 3 lugs cutout, all same size. There is general consensus on this too but note again that an experienced member believes the single cut-out came earlier; may have been as early as 1972.
1974: Cutout in bottom headlug only.
1975: Cutout in bottom headlug only.
So this is either a 74 or 75

Fork Crown:

1974: IC crown, club in top of each side of crown.
1975: IC crown, club and "COLNAGO" on top of each side of crown. There were numerous contributions supporting this but again, a experienced member took the time to write "This is too early for the *Colnago* in the crown. I think that came in by 1977 or so. The first generation Mexico's had no "Colnago" in the crown, and their first year was 1975...earliest possible year for the Colnago stamp in the crown would be 1976, but I'm betting it was later than that.

So this may be a 1975, but most likely a 1976+

BB:

1975: Club cutout in BB shell.

(this is not shown here and a good thing for the OP to check)

Braze-ons:
197? & earlier: none except chain stay derailleur cable stop check
197? - 197?: Above plus over BB cable guides check
197? - 197?: Above plus shift lever mounts check
197? - 197?: Above plus one set DT water bottle mounts check
19?? - 19??: Above plus ST water bottle mounts No
1976/77: Above plus first appearance of two TT brake cable guides (note that the "Colnago" cast into the fork crowns definitely happened before the addition of TT brake cable braze-ons). No

Don't you see any inaccuracies here?