Even if Sharp did not have his own copy of Child prior to 1916, I am sure he would have consulted a copy in the BM, as he was a visitor there to consult copies of Playford, for example. Or perhaps he just needed to consult a copy of Child in the USA as his own copy was in UK. Is his own copy still in VWML?
Regarding Wagner, Karpeles writes, in the biography, that he was almost as enthusiastic about mathematics as about Wagner, while at Cambridge (p. 6), and "as with most young musicians of his day, Wagner was his god." (p. 13),this was 1892. He quoted Wagner in love letters to his intended wife, Constance, (p. 16). Daughter Dorothea's third given name was Iseult and son's second name was Tristan, (p. 18). Methinks Sharp was something of a fan of Wagner!
Derek