Just spotted your thread on OTD. Interesting watch and should date to around 1962/63 but I am not convinced it is right as it should have dauphine hands not the hands you are showing. The print on the dial is was also adopted later. Early UG compax had an applied U sign and applied silver batons. Check the movement and see if it is marked 130 or 85. The earlier should also have a berguet hairspring which was discontinued with calibre 85 (both based on the valjuoux 72).

You are right about references. The first number is the reference or model and the second number is the serial number. Serial numbers were 5 digit until around 1963-64 when they went to a six digit serial number.