The idea that the architect for Sudley was John Whiteside Casson derives largely from a family biography of the Robinsons (Nicholas was the first occupant of Sudley c.1824) which says that the architect's name was "Daddy" Carson. No Carson is listed under the heading of Architect in the contemporary directories but there is a Casson. Some people, myself included, think this is near enough.
This came to mind when I found the gravestone of (probably unrelated) Betsey Caſson in St James's cemetery, her name apparently halfway between Casson and Carson. So which is it?
Well, it turns out that early C19 English (and other languages) were still using something called the long s (highlighted in the closeup) which looked like a stretched r and was generally used as the first character in a double-s (other usage also applied). The practice largely died away by the mid-C19 but it may well be the source of confusion at Sudley over spelling Casson (and, elsewhere, Moss).