I'm sure literary critics have written a lot about the status of inaccurate but purportedly factual information in fictional works. It seems like a simple question with a simple answer in many ways, right? Fiction is fiction hence Dorothy Sayers' "Author's Note" prefacing Gaudy Night:
"It would be idle to deny that the City and University of Oxford (in aeternum floreant) do actually exist, and contain a number of colleges and other buildings, some of which are mentioned by name in this book.... Persons curious in chronology may, if they like, work out from what they already know of the Wimsey family that the action of the book takes place in 1935, but if they do, they must not be querulously indignant because the King's Jubilee is not mentioned, or because I have arranged the weather and the moon's changes to suit my own fancy. For, however realistic the background, the novelist's only native country is Cloud-Cuckooland, where they do but jest, poison in jest: no offence in the world."
Of course the question is a bit more complicated and can seem relevant in terms of poetry as well as prose, as this exchange among fictional characters in David Lodge's novel Nice Work suggests:
"Marion began reading her paper in a low monotone. All went well until she observed that the line from 'Locksley Hall,' 'Let the great world spin for ever, down the ringing grooves of change,' reflected the confidence of the Victorian Railway Age. Vic raised his hand.
"'Yes, Mr. Wilcox?' Robyn's tone and regard were as discouraging as she could make them.
"'He must have been thinking of trams, not trains,' said Vic. 'Train wheels don't run in grooves.'
"Simon Bradford gave an abrupt, high-pitched laugh; then, on meeting Robyn's eye, looked as if he wished he hadn't.
"'D'you find that suggestion amusing, Simon?' she said.
"'Well,' he said, 'trams. They're not very poetic, are they?'
"'It said the Railway Age in this book I read,' said Marion.
"'What book, Marion?' said Robyn.
"'Some critical book. I can't remember which one, now,' said Marion, riffing randomly through a sheaf of notes.
"'Always acknowledge secondary sources,'* said Robyn. 'Actually, it's quite an interesting, if trivial, point. When he wrote the poem, Tennyson was under the impression that railway trains ran in grooves.' She read out the footnote from her Longman's Annotated edition...."
(Penguin paperback edition, 1990, pp.242-243).
So what would the annotated edition to Carole Nelson Douglas' Sherlockian/semi-Sherlockian novel Castle Rouge say about this passage in which the possibility that a Jew was Jack the Ripper is discussed?
"Irene [Adler] supported Bram [Stoker] as well. 'That is one fact [apparently ritualized arrangement of the victims' bodies] that made the Jews suspect of the crime: they perform ritual sacrifice of animals, and so were favored suspects because the women were killed as if in a ritual." (Forge Books, mass market edition, 2003, p.281)
In my imaginary landscape of the Sherlock Holmes world, Irene Adler is Jewish** but that may not be how Carole Douglas conceives the character. But earlier in the novel an indisputably Jewish character says:
"He shrugged. 'Who am I to judge ways of worship? At Passover we celebrate with the sacrifice of the lamb. Christians do not understand that, yet they worship a sacrificed man." (Ibid., p.73)
The convoluted plot of this "novel of suspense featuring Irene Adler and Sherlock Holmes" is not too important here. I won't reveal the plot but suffice it to say that it turns out that Jack the Ripper is not Jewish.
I can think of a few scenarios here, all of which are perplexing and a bit weird:
1) Carole Nelson Douglas, an actual person living in the 21st century, thinks that Jews in the 19th century engaged in animal sacrifice.
2) Carole Nelson Douglas knows full well that actual (real) Jews in the 19th century did not engage in animal sacrifice but has invented a Cloud-Cuckooland of 19th-century Europe that maps onto historical 19th-century Europe in some respects and not others. In this fictional version of 19th-century Europe, Jews engaged in animal sacrifice.
3) Carole Nelson Douglas knows full well that actual Jews in the 19th century did not engage in animal sacrifice. But she has invented fictional characters who know that Jews did not engage in animal sacrifice but who, for whatever obscure fictional motives, wish to suggest to their fictional interlocutors that Jews in the 19th century do engage in animal sacrifice. [This one seems highly implausible as the plot is not furthered by any such devious scheme.]
Given that the Jewish Jack the Ripper theory is introduced in this mystery mainly as a red herring, #1 seems most likely. One could argue that the Jewish Jack the Ripper theory functions as more than a red herring since Irene Adler is initially set on the case by the Baron de Rothschild who is concerned about antisemitism. Thus anything that makes the possibility of a Jewish Jack the Ripper more plausible does serve the plot and thus #2 may be the answer. Arguably, however, this rather subtle plot point would be established more effectively (and way less subtly) by putting these notions only into the mouths of non-Jews.
Perhaps Robyn Penrose would tell me that it's a "trivial" point, but nonetheless, I would like to know whether a popular American mystery writer does or does not think Jews in the 19th century engaged in animal sacrifice.
**I have no good Sherlockian evidence for this, either from within the canon or from pastiches, but it just seems like she ought to be Jewish.