What i can tell you is that it is from 1968 and was bought new by my dad for his dad, sadly my grandad has passed now, i even have the original box & Papers but they are at home. I am told it is an ST1310019 but i have never seen another with a blue dial. Any help would be greatly appreciated guys.
Ref 131.0019 is a Genève and your appears to have a refinished dial. This reference has a caliber 601 hand wind movement.
I read that could be a Geneve but i was not sure... My dad says that the dial is original, as when my dad bought it he worked for an Omega AD
The case may be a 131.0019 and the movement may be a Cal 601. The dial is not. The words SWISS or SWISS MADE appear to be missing as does the Geneve. I don't know if its the camera angle but the dial seems to be wonky in the case.
Its the camera angle, its straight. Thats what i thought but i know that watch is as original as it gets as my dad bought it new for my grandad and it has never been anywhere else - Strange. Next time i'm in Switzerland i will take it to Omega to see if they can help.
The only other possibility I can come up with is maybe this was a company presentation watch and the dial was meant to have a company name or logo printed in the space under the hands? Its not inconceivable that your Dad got hold of a blank one for a good price, especially if he worked at an AD. If you have the provenance that shows that it is all original then I guess it is.