Grief, those are a bit odd! Have you got sizes, Max? Is there gilt on the edges? Think I've got all the sizes/shapes sorted now, so this might confirm it.
One thing did occur to me; there was a company called Sherdley who at around the same time was trying to emulate the success of Swirl and I'm wondering if this is an example of their work? Might be a significant find all the same.
On another point: there is no confirmed evidence that Casson did design Swirl! Might be one of these urban myths that's been perpetuated by eBay and I'll admit I always thought it was her design, but neither LJ's nor Nigel's book actually attribute it to anyone.