OK, I don't have detailed knowledge about Sowerby designs, so stop reading now if you don't want to see an uneducated opinion/question.
When I read this post initially, the Sowerby Elephant handled bowl didn't even cross my mind - it was so different.
The swan and elephant butter dishes have a sleek, elegant, unfussy design, which I find hard to match up with the Sowerby elephant handled bowl.
The the bowl is quite a heavy, clumsy looking thing, with the handles modelled as elephant trunks. Why are such different handle designs used? One wouldn't put the butter dish and bowl together as part of the same design visually. The only matching feature is the leaf pattern, which Bernard pointed out.