Many data points to cover. I'd like to start with offering some of my perspective on the Josiah Quincy account, and explain why, from a Bayesian view, it's not as reliable as we might have expected.
The following is an excerpt from this post of mine: https://meditationsandmeaning.blogspot. ... leged.html
Quincy's account of his visit to Nauvoo, which took place shortly before Joseph's Martyrdom, was published in 1881 and 1883 and compiled from Quincy’s journal entries and letters written in 1844. Quincy was certainly not acting as a scribe for Joseph during the visit, and it seems doubtful that, by the time Quincy sat down to compose his journal entries and letters concerning the variety of experiences he had at Nauvoo, that be actually would have recalled the exact words which Joseph had said. Rather, he seems to be caricaturing the types of things which were said in order to convey the general spirit of his experience. For instance, he says Joseph Smith's mother purchased the papyri, which is not true, and that the price was 6,000 dollars, which is also not true. Here it looks like Quincy combined two separate ideas - that the papyri had been purchased and that Joseph's mother owned them - into a single claim. And he did so without attention to the finer details."And now come with me," said the prophet, “and I will show you the curiosities." So saying. he led the way to a lower room, where sat a venerable and respectable-looking lady “This is my mother, gentlemen. The curiosities we shall see belong to her. They were purchased with her own money, at a cost of six thousand dollars.” and then, with deep feeling, were added the words, "And that woman was turned out upon the prairie in the dead of night by a mob " There were some pine presses fixed against the wall of the room. These receptacles Smith opened, and disclosed four human bodies, shrunken and black with age. “These are mummies" said the exhibitor “I want you to look at that little runt of a fellow over there. He was a great man in his day. Why, that was Pharaoh Necho, King of Egypt!” Some parchments inscribed with hieroglyphics were then offered us. They were preserved under glass and handled with great respect. “That is the handwriting of Abraham, the Father of the Faithful" said the prophet "This is the autograph of Moses, and these lines were written by his brother Aaron. Here we have the earliest account of the creation, from which Moses composed the first book of Genesis." The parchment last referred to showed a rude drawing of 2 man and woman, and a serpent walking upon a pair of legs. 1 ventured to doubt the propriety of providing the reptile in question with this unusual means of locomotion…
Based on that false understanding, words were invented and put into the mouth of Joseph, i.e. “they were purchased with her own money…” Obviously, that doesn’t bode well for the rest of the account.
Quoting Joseph's exact words was evidently not Quincy’s concern. Since, in his words, “the blasphemous assumptions of Smith seemed like the ravings of a lunatic."
Are the “ravings of a lunatic” significant enough to remember word-for-word? He even compared Smith to inmates at an insane asylum: “victims of the sad but not uncommon delusion that each had received the appointment of vicegerent of the Deity upon earth." Quincy does not seem to hold this against Smith personally. but rather is taking pity on him while at the same time marveling that such a man could accomplish all that Joseph Smith had accomplished.
Moreover, Quincy’s journal entry is less reliable because it was apparently rewritten decades later to make it more suitable for publication.
In his introduction, Quincy states:
This may help explain why the name “Onitas,” which other witnesses consistently identified as the name of the male mummy, does not appear but is replaced with the name of Pharaoh Necho. We might note that “O” and “N” are the most prominently pronounced sounds in both names, which may have either prompted a change geared more toward the interest of the audience, or may have caused Quincy to incorrectly recall. In any event, no other account has Joseph speaking and behaving the way he is depicted in this account.... a friend, who had read my journals with interest, offered me his most valuable aid in what may be called the literary responsibilities of the undertaking. My narratives have gained in grace of expression as they passed beneath the correcting pen of my obliging critic, and I am confident that a stern exercise of his right of curtailing reflections and omitting incidents has been no less for the reader's advantage.
We might reasonably suppose that any of Joseph Smith's detailed, clarifying remarks, which Quincy may conceivably have originally written down, would have been edited out as part of that "stem exercise of his right of curtailing reflections and omitting incidents."
In further support of this view is the included statement, “This is the autograph of Moses, and these lines were written by his brother Aaron. Here we have the earliest account of the creation, from which Moses composed the first book of Genesis." Since this was May of 1844, Joseph had long since already translated both the Book of Moses and the Book of Abraham. But Quincy and his friend appear not to realize that the Book of Moses had in fact come from a translation of the Bible, not from translation of the papyri. So in print, it ended up in a narrative of the papyri - and this is perhaps the type of liberty which Quincy calls the “grace of expression” in the introductory excerpt to his book, cited above.
Why would Joseph tell Quincy things which contradicted the consistent narrative he told others?
Especially in front of his mom? And in reference to things which townspeople could have easily contradicted if Quincy had spoken with them?
Would that not put Joseph’s narrative in jeopardy?
Are we to believe he did not know, or did not care that he was putting his narrative in jeopardy?
If Joseph did indeed say those things, it would make sense if he was joking around and jovial, in which case the statements should not reflect his actual claims about Abraham.
The fact is, the Quincy account contradicts Joseph’s usual narrative on a number of points.
If Quincy’s account is to be seen as evidence of anything, we must acknowledge that the evidence was tampered with. The conceptual chain of custody of the account was poorly kept, as Quincy himself conceded - i.e. his letters and journals were altered so as to “gain in grace of expression,” etc.
It would not be allowed as evidence in a court of law.
Moreover, Quincy admitted his letters and journals had been altered nearly 40 years after the events in question, before publication.
And, the person who altered them was someone who presumably had not been present during the encounter with Joseph Smith and would have had no personal knowledge of the events.
A couple questions now, to aid your Bayesian analysis regarding the reliability of the Quincy account:
Question 1: Would the Quincy account have been more reliable if it did not contradict the consistent narrative elements found in other eyewitness accounts?
Question 2: Would the Quincy account have been more reliable if it had not been altered?
Question Second Amendment: Would it have been more reliable if it had been altered only one year after being written, rather than almost 40 years after being written?
Question 2b: Would it have been more reliable if it had been altered by someone who had personal knowledge of the events, rather than someone with no personal knowledge of the events?