Thanks for your input. I realize the odds but there is always that 0.1% possibility ;)

Can you tell me anything about the hand engraved serial number on the edge of the case back?
It starts with CP198.

: Jo Siffert sold a mere handful compared to other distributors in
: Switzerland, so it's not really that probable. In fact, as he
: was not an authorised distributor in the same sort of way, the
: watches he sold may not have had the Cuanillon marking. It's
: vastly more likely that your watch was sold by a jeweller or
: watchseller than by Siffert, I'm afraid.