I have located a genealogy for Wilhelm von Closen, though. He married and had children, and the family remained located in and around Schramberg for almost another century, before one branch emigrated to England in 1908. They had a daughter, Elsa, who went on to marry a man by the name of Michael Keay in 1920. In 1924, they had one daughter, whose name was Mary Keay. This may be simple coincidence, but… it concerns me.
The Mary Keay Jonathan is referring to is mentioned before in episode 4. She is the bald, tattooed woman who owns the 'Pinhole Books' bookshop, which houses a number of cursed books.