OK, I realise that few people are likely think, muse or wonder thus — even my mother the Heyer fan, when I rang her excitedly to tell her my discovery, didn't remember the books or characters involved.
According to Heyer's biography, I was right — and that's why Heyer named the book These old shades (shades = ghosts). She was reusing her characters! Now that I know that, I suddenly recognise the Black moth's very vanilla hero and heroine as Jenny and husband in These old shades; likewise, the villain's best friend is the same character in both.
It makes me glad, because I always wanted to know what happened to the Black moth villain. I wonder why Heyer changed the characters' names — unless she didn't want the new book associated with The black moth.
I don't really have a point here; I just found it interesting that a best-selling author can actually do that and get away with it. I guess others have as well. Austen certainly has reused her plots and characters, if not as obviously (and probably not intentionally); and I'm sure there are many others out there that don't spring to mind immediately.
But I just wanted to comment on that, for any Heyer fans out there. Want to read more about the characters — or the villain — in The black moth? Read These old shades and see what happens to them later.