In 1972, Eddy Merckx decided to attempt the Hour Record. A special road TT bike was constructed to test the various ultra-light tubing, frame angles, etc. for the track machine. On Oct. 25, 1972, he set the new Hour Record. The bike was a special track Colnago with usual Merckx's name on the down tube but a reflective Windsor (Mexico) bike company's decals were placed on head and seat tubes. This caused a rift between Merckx and Colnago for the 1973 season and Merckx left Colnago for De Rosa. Due to saddle boils/injury, Merckx was mostly inactive in 1973, but he appeared in a Columbus tubing advertisement with Ugo De Rosa holding up his usual orange road machine. This caused a stir on who built the Hour Record bike at the time.
To settle the matter, Ernesto Colnago made a new model in 1974, Colnago Mexico, with a new decal that clearly stated who built the Hour Record bike on the seat tube and the chain stays. This model had the Columbus Record tubing and was available in both road and track versions. It ran from 1974 thru 1979. To commemorate the end of the limited model run, Colnago built a special Mexico road bike in 1979, the completely 24kt gold plated Colnago Mexico Oro frame set bicycle to present to Pope John Paul II (he later exchanged it for a white Colnago Arabesque Gentleman). Five replica completely 24kt gold plated Colnago Mexico Oro frame sets were also built at this time for very special customers. The stamped identification in the frame and the steering column are unlike any other serial numbers of other Mexicos or Mexico Oros. These are the only Colnago frame sets to be considered the Colnago Mexico Oro. Due to being "lost in translation", Colnago Super, Mexico, Mexico "Mosca", Moscva Crono, with gold plated fork and stays were often referred to as Colnago Mexico Oro when these partially plated Colnagos should be referred to as Colnago Oro. Also later gold plated Colnagos were being confused with Colnago Mexico Oro, e.g. King of Spain's Colnago Oro (it has a Precisa fork). Currently there are three known 1979 Colnago Mexico Oro: one in Cambiago, one in Chicago, one in Sao Paulo. There were fake ones spotted in Germany, Australia, and France.
In 1980, there was a Colnago Mexico "Mosca" (aka Colnago 2000), a Team Time Trial bike created for the Team USSR. The right title would be Mosca 1980 Quartetto Olimpionico 100km con l'aerodinamica bicicletta which was labeled Colnago Mexico on the chainstays but obviously, they were entirely different from the Merckx model. It had a 650 front and 700 rear as well as 24mm seat post diameter and 17mm handlebar stem. Some of this model came with gold plated stays and fork and were sometimes also referred to as Colnago Mexico Oro confusing things even more. There is also a bike that is confused with the Colnago Mexico "Mosca", the Moscva Crono (1980 - 1982) which is easy to spot because it has seatstays that end at the middle of the seat tube and they do not end at the seat lug like the "Mosca", chainstays that are now stamped "Colnago", multi-shaped tubes, and lug within a lug in the BB. It does retain the 24mm seatpost and the 17mm handlebar stem and the uni-crown fork with brazed reverse brake bolt. Some of these also came with gold plated stays and fork and were referred to as Colnago Mexico Oro. FYI: The Campagnolo OEM Colnago aero seat post on these bikes were made aero by milling a solid seat post flat on the sides and retaining the round bottom where it fits into the seat tube and these were not pantographed but just had a small Colnago decals on both flat sides. These are not to be confused with the small round seat post for Colnago Oval CX.
To even confuse things further, also in 1980, a new Nuovo Mexico (catalog name only, no label on the frame) model was started using the crimped tubing at top and down tubes. These new Colnago Nuovo Mexicos had nothing to do with Merckx but more to do with the beginning of experiments with crimping and tube shapes which ultimately will result in the Gilco (GILberto COlombo) tubing with Columbus and should be considered the first of their own kind. Guiseppe Sarroni should be associated with these Nuovo Mexicos since he took them to victories. The Nuovo Mexico with anti-vibrant fork is not to be confused with the Profil (1982-1983) which has a main triangle with all tubes crimped with CX fork or the Profil CX (1984-1985) which is the same as Profil but with aero shifter bosses on the top of the down tube. To confuse the matter even further, the old Mexicos were still being delivered into the1980s due to Colnago's notorious delays in filling orders on time or frame sets languishing in bike shops for years before being sold.
Basically the Merckx Colnago Mexicos (1974-1979) had round superlight main tubes, Sarroni Nuovo Mexicos (1980-1985) crimped top and down tubes, ESA Mexicos (1986-1988) had 6 ribs on main tubes, Zoetemelk Mexico SR/CRs (1985-1986) had a crimped top tube with a 4 rib downtube. FYI: Master with 4 ribs, Tecnos with 5 ribs, Conic with 8 ribs, and Regal (ESA Mexico w/Arabesque lugs) with 6 ribs. The visible difference between 1974-'79 Mexico and 1974-'79 Super is that the Mexico has chainstays that are not crimped at all (round-oval-round). FYI: Masi (round-D-round), De Rosa (round-diamond-round). Note that the timelines are for the USA.
It has been noted that there have been fake Merckx Mexicos which were actually Supers with chainstay crimps being filled in with automotive body filler and repainted. Repainted frames are usually fakes, damaged, or undocumented originals. Always start with the fake frame and let the seller prove it is real or undamaged and that it is not stolen. Most people cannot prove the provenance of their frames or their ownership and as such it is rare to see vintage/classic bicycles at auctions by the major auction houses. Remember that there are lot of unemployed frame maker's staff and lot of small foundries/machine shops who lost their orders when the bicycle frames went to aramid fibers. And guess what? They are now producing beautiful fakes in Germany, Holland, Poland, Romania, Italy, etc. for sale on eBay. I love it when they try to scratch the decals and promote rust. And you have to love the Germans with their precision, the paint and the chrome are beautifully done, unlike the Italians with their vino breaks. Authentic old Colnagos look like they were touched by a human hand, file marks in the chrome, uneven paint, etc., instead of a machine. The fake Mexico Oro in France was interesting in that the steering column was horribly done, BB area had gold paint, and the wrong type serial number was proudly displayed. The fake Mexico Oro in Germany was even more interesting, don't they know that gold doesn't rust? A good way to spot fakes is the placement of the decals, measure the distance on a known Colnago and take a look on the questionable frame.
Another is the cheap mixture of components, most Colnago owners upgrade as the years go by to components reflecting the value of the bike frame or had the best equipment at the beginning since they could financially afford Colnagos. The fakers just want to maximize their profits so are not going to spend more money. Another trick is a fake Colnago chainring added to a Campagnolo NR crank arms. Originals came as a set with Colnago pantographed crank arms from: OMAS (OEM Colnago Mexico crank set), Campagnolo (Campagnolo Colnago pantographed crank set and Campagnolo Colnago pantographed Mexico style crank set), Gran Premio della Montagna (GPM-Gipiemme Colnago pantographed Mexico style crank set) and Ambrosio (Ambrosio Colnago pantographed 6-pin crank set [ not to be confused with Gipiemme Cronospecial 6-pin] ). FYI: OEM (Original Equipment Manufacturer) were made especially for Colnago and were not available as a non-pantographed regular line item under the manufacturers name. FYI: OEM Colnago Mexico crank set was available with OEM OMAS Colnago Mexico BB (titanium spindle/bolts, alloy adjustable cups, sealed french bearings). FYI: All Colnago pantographed crank sets, with the exception of early '70s ones, came with OMAS black anodized alloy chainring bolts and all had no dust caps. FYI: All Mexico style cranks came with a beveled cut-out 5-pin and polished reduced arms (note that the Campagnolo Colnago pantographed cranks for Supers pre-dates the Mexico styles and do not usually have the machining/polishing but has the pantographing, usually vertical, and cut-out Campagnolo chainring with just a clover, no C).