Another vintage Omega for identification

The s/n dates the movement to the late 40s, but I'm not sure if the number on the inside of the case back is the reference number, or just a case serial number. I wasn't able to locate anything similar online for the W160706 number. Also, when did manufacturers use import codes on their movements? I expected to see one on this movement. I know that topic has been addressed many times, but I thought import codes were used from the late 30s through the 60s. I suppose this watch might have been purchased outside the US.
Thanks

Nice watch. Get rid of the red hand. Swap out for a blued steel one