I don't think
Bo fits in this list. I think it's one of those nicknames that are used for many names. Just because some Williams are called
Bo, it' doesn't make
Bo a nickname for
William.
As for
Karen: it's definitely a variant, two mutually exclusive names. English-speaking Katherines don't get called
Karen, the same way Marias don't get called
Mary (anymore).
Alexandrina, Annabella, Clementine, Charlotte, Emilienne, Florence, Frederica, Katharina, Mary (May), Maud, Penelope, Rosamund, Theodora (Teddy).
Aubrey, Axel, Benedict, Bertrand (Bertie), Cuthbert, Dashiell, Everard, John (Jack) Leopold (Leo), Magnus, Matthias, Maximilian (Max), Wilfred.