You’ve lost me somewhere there Rick! While I in no way whatsoever want to get into a debate about when such things “should” be marked, as I have every confidence in your ability to tie any argument into knots and be correct at the end of it all, I think the point remains that the most recent century change was certainly celebrated at the end of 1999/ beginning of 2000. Therefore to come across something in a novel very obviously different does jar the reader, at least one who knows when Queen Victoria died. So either, as you suggest, you have to justify this somewhere in the text and preferably before your reader puts down the book to research this puzzle, or at the very least in the historical end-notes. Or you change your story ever so slightly to avoid such a jolt in the first few pages. Admittedly my research into this didn’t get me very far, but I didn’t come across any evidence that the author was factually, if not fictionally, correct. There was some suggestion that in America there was more of a consensus that 1900/1901 was the right time to celebrate, but nothing to say that this occurred in Britain. So I reluctantly concluded this might have been a mistake on the author’s part.