No one know what the markings mean yet - although there have been many “S/xxxx” watches found. They have as far as I recall always been found in lesser tier brands though, which just bring me on to comment that you watch is not a Breitling, The dial is reprinted and the serial number does not correspond to Breitlings year nomenclature. The lowest known Breitling serial number is about 563000. Often old watches are redialled to try to give them more value.