I have not had the time to work through these four messages, but want to make a very quick point: The dials also seem to be different between the Pasadena and the non-Pasadena (in addition to the presence or absence of the "Pasadena").

Look at the markers at 3-6-9-12. Pasadena has angular markers (rectangular), we can call them "dashes" / non-Pasadena has smaller dots. I have been checking these, as I have spotted them, for the last two weeks, and have not seen any exception to this pattern.

Jeff

++++++++++++++++++++++++++++

: With this paragraph Stewart, you've solved the riddle whether you
: know it or not!

: It was Heuer's model code schema putting them into a bit of a fix.
: The terminal numeral of the numeric code usually denotes
: material, in these six digit codes as well as the four digit
: ones, with some exceptions like the divers. 3 is most common,
: and denotes steel, 5 is gold plate, 8 is solid gold and 1
: denotes a PVD finish.

: In calling the PVD 750.501 a Pasadena and the steel 750.503 a
: Montreal, a problem arose when they wanted to produce a steel
: Pasadena. Logically, that model would be a 750.503, but that
: number was already taken by the Montreal. Looks like the
: compromise was to append a -3 to denote a steel case to the
: existing 750.501 code for the Pasadena and differentiate it from
: the existing Montreal. Hence 750.501-3.

: Makes complete sense to me now.