Ah, yes, I had thought of that, as several of my ancestral lines in Sweden do not have a "technical" surname until much later (1890's, 1900), when they either just kept the father's name (Johansson, for example) or took it from their village or their work.
I do know Sven (or Svante, as he sometimes calls himself, old style) was apprenticed to a Master Zetterbom or Zetterstrom (I forget the exact name at the moment), so he's not taking Cantzoff from him. This doesn't mean, of course, that he didn't adopt Cantzoff from an earlier master. Sven was about 35 with Zetterbom; I would assume he had some experience beforehand.
This opens up another line of inquiry! Thank you so much for taking the time to write. I appreciate all this help and discussion, very much.