Hi Jill
Yes you have failed

,but then again, so have the rest of us!

No, I can't find a marriage cert for his parents, James & Fanny (or Harriet). The reference regarding Thame comes from the 1891 & 1901 census. Both census are specific in that James (snr) came from Cheltenham, Glos, Fanny from Chalvey, Bucks & James (jnr) or William James from Thame, Oxon.
Emma was just a possible connection from the other thread. I don't believe it is relevant.
I have James (snr) Naval records and they don't make great reading. During his 9 years of service, he spent 4 periods in the ships cells, he was court martialed for 2 years from 1879-81 in Lewes. He finally left the Navy in 1883 when he was invalided from the Naval Hospital at Haslar.
My gut feeling is that he then met Fanny between 1883 & 1887. They had a son out of wedlock and the birth was never registered. Given his navy record, I'm not surprised he didn't do anything by the book.

The Selwood family I am tracing came from the Gloucestershire area.
I really think this mystery is going to remain unanswered, but I will keep trying.
Thanks again for your help, Jill.
Regards
CB1964