[JoepeteJokla]

On the movement, underneath the 4520A number, there is another number with 6 digits. Should this number match the caseback number ?

 

[Pei Der Han]

On the movement, underneath the 4520A number, there is another number with 6 digits. Should this number match the caseback number ?

I don't think so since the movement was likely used in more than one case style.

Not sure but it could be a movement serial #; Seiko was still formalizing markings throughout the watches in those days and may have been emulating some of the better Swiss watch makers.

I'm sure that someone more knowledgeable will either verify this or give a proper description of what the 6 digit number represented ;D

 

[7s26b]

I think this is a chronometer grade movement,therefore each one would be numbered to indicate the person who made the movement and it's records of accuracy. I would imagine this wouldbe a "factory only repair " item- so warranty records of the movement would be needed.