Nicholas, I've dug up a reference here that seems to me to indicate that marriages between a British national and a Japanese national conducted under Japanese law (lex loci) were not recognised as valid under British law until 1899, and even then British nationals living in Japan were not advised of the changes until much later. https://books.google.com.au/books?id=S6z2b44ksNUC&pg=PA395&lpg=PA395&dq=marr iages,+yokohama&source=bl&ots=hm3jnjbFjq&sig=11kNE86nVImKS7b8MpyKwMlHCXM&hl= en&sa=X&ved=0CCYQ6AEwAjgKahUKEwib392c_7bHAhUo3KYKHWiXCh0#v=onepage&q=marriag es%2C%20yokohama&f=false (page 395) It would seem to me from reading this reference that if the Trevithicks married according to Japanese marriage law, that is in a traditional Japanese ceremony rather than in a recognised Christian church, their marriages would not have been reported to the Registrar-General in London by the British Consular authorities in Japan, even if those authorities knew about the lex loci marriages.