Nice bit of work Stewart, it's always good to see someone doing some research on the Heuers, particularly lesser known ones like these.

As far as the "non-" goes, I always read it as shorthand for, for example, non-Pasadena Pasadena, i.e. a Pasadena without "Pasadena" written on the dial. It just feels a bit redundant to write the model name twice so for ease of use it just becomes "non-Pasadena".

The 750.503 Montreal was also available with a blue/blue dial too as the 750.503 B as well as the 750.503 N, so that's one to add to the list - it's missing from the OTD MOAT too.

Not sure about the 1-3, do we have any pictures to go on? I'm just finding 501s and 503s in pricelists.