Davidfor, thank you for reminding me about the "previews". Because I run with a patched system, only use Calibre, and never enable wifi, they never have been visible. The Calibre driver settings were right (previews box not checked). Following on the suggestion you gave in this thread
Kobo books not deleted from device, I reset the account on the Clara and then resynched with Calibre. The ghost series are gone now. Whew.
Thank you!