I just spoke with the owner and she said the service papers from the jewellers gives the number 20067, nothing else, so I guess that is just the serial number. I will try and get a look at it over the next few days and pop the back for a quick inspection and photo, thanks.

: Confirmation of the movement would be interesting then. The 18K
: models we know of, like the 416 and 418 are 13 ligne models
: whereas the 333 that your dial most closely resembles is 14
: ligne. It's entirely possible that there were 14 ligne 18K
: watches, it's just that they're not shown in the catalogues we
: have.