Anne, Raymond Notley's book quote confirms and adds to the Ivo Haanstra quote I mentioned earlier, and yes the patterns Ivan and Marcel certainly look like a possible match although I can't see too clearly. That advert is said to be from 1916, with an imminent ban on imported domestic items soon ahead, the ad is said to have an urgent tone, which ties in with the factory being in France, and also perhaps Lang exporting to Australia?
I think I may have read somewhere that design registrations only last 25 years before copyright runs out? This was regarding some Whitefriars designs so I don't know how relevant that info is for these designs but, if Sowerby moulds were purchased 1905, Jules Lang could have registered 24 years later in 1929, assuming Sowerby Registered them pre 1904. Hmmm...