Re: 1969 Cinelli SC
You are correct in you speculation Old Ned.
Windsor was a prominent bike boom brand in the Americas and the Profesional, the Spanish spelling, was there top model. It has been branded "The Mexican Cinelli" because to the untrained eye it looks exactly the same as a Speciale Corsa. In fact they are very similar with the main differences being the location of the serial number, the fork crown, set post size and number of drillings in the head and seat lugs. Many a repainted Windsor has been sold over the years as a Cinelli. The Windsor was a very decent bike and the company brought frame builders from Italy to set up their Mexico City factory. In the end inconsistent product quality doomed the brand and the Profesional ceased in the early 80s. Windsor has been revived recently but I am unaware of any connection to the original builder.
Attached is a quick visual comparison between the Windsor and the Cinelli