Let's start with W. W. Phelps, Joseph's scribe, from a letter dated July 19-20, 1835:
"The last of June, four Egyptian mummies were brought here; there were two papyrus rolls, besides some other ancient Egyptian writings with them. As no one could translate these writings, they were presented to President Smith. He soon knew what they were and said they, the "rolls of papyrus," contained the sacred record kept of Joseph in Pharaoh's court in Egypt, and the teachings of Father Abraham.
Dr. James R. Clark of Brigham Young University writes:
Between October 1 and December 31, 1835, there are fifteen individual entries in Joseph Smith's journal referring to the papyri, the mummies, and/or the records. Six of these entries call the papyri "Egyptian records." Six additional entries refer to the collection as "ancient records" or "records of antiquity." In another entry he calls them simply "the papyrus." Only in one entry does Joseph Smith refer to them as "sacred records." The important point here seems to be that while in July, 1835, Joseph Smith referred to one roll as containing "the writings of Abraham" and "another the writings of Joseph of Egypt," in subsequent references during the three month period when he was working most intensively with them he spoke of the papyri simply as "Egyptian records" or "ancient records." These numerous entries should at least raise a caution against any assumption that the entire collection of papyri that Joseph Smith had was exclusively the record of Abraham and Joseph. The fact that these two documents were considered most important by the Prophet may have led to that faulty assumption.
How many "rolls" (leaving aside the "other ancient Egyptian writings) were there? Only two, those dealing with Abraham and Joseph? A non-LDS newspaper, gives us a clue, from an article that appeared in the March 27, 1835, edition of the Painesville Telegraph:
There was found with this person [mummy no. 1] a roll or book, having a little resemblance to birch bark; language unknown. Some linguists however say they can decipher 13-36, in what they term an epitaph; ink black and red; many female figures.
[Mummy] No. 2 ... found with roll as [mummy] No. 1, filled with hieroglyphics, rudely executed.
[Mummy] No. 3 ... had a roll of writing as No. 1 & 2....
And further, what happened to the book of multiple leaves and another book found in the arms of one of the mummies, as mentioned by the Cleveland Whig in March of 1825?:
There was found deposited in the arms of the old man referred to above, a book of ancient form and construction, which, to us, was by far the most interesting part of the exhibition. Its leaves were of bark, in length some 10 or 12 inches, and 3 or 4 in width. The ends are somewhat decayed, but at the centre the leaves are in a state of perfect preservation. It is the writing of no ordinary penman, probably of the old man near whose heart it was deposited at the embalming. The characters are the Egyptian hieroglyphics; but of what is discourses none can tell....There is also another book, more decayed, and much less neatly written - its character and import involved in like mystery.
All the more delicate fragments that were mounted on glass panes appear to be only a small remnant of the original corpus. For example, we have the testimony of Charlotte Haven, a non-LDS visitor to the city of Nauvoo in 1843:
Then she [Mrs. Smith] turned to a long table, set her candlestick down, and opened a long roll of manuscript, saying it was 'the writing of Abraham and Isaac, written in Hebrew and Sanscrit," and she read several minutes from it as if it were English. It sounded very much like passages from the Old Testament - and it might have been for anything we knew - but she said she read it through the inspiration of her son Joseph, in whom she seemed to have perfect confidence. Then in the same way she interpreted to us hieroglyphics from another roll. One was Mother Eve being tempted by the serpent, who - the serpent, I mean - was standing on the tip of his tail, which with his two legs formed a tripod, and had his head in Eve's ear.
In 1906, President Joseph F. Smith, while visiting Nauvoo, told Preston Nibley of a childhood experience in which he observed "Uncle Joseph" working on a copious quantity of papyrus roll, which "when unrolled on the floor extended through two rooms of the Mansion House.
Other significant variations in the nature of the original documents and the fragments left to us could be multiplied, but the eyewitness accounts of both the quantity and nature of the texts would seem to pose significant difficulties for critics presently laboring intensively over fine details of the KEP. A substantial quantity of the original corpus is missing, and this, and only this, has provided the critics, especially the most disparate of them, the opening they needed for the construction of novel and highly technical theories of Book of Mormon translation. These efforts, however, are ultimately of little weight, since none of the text critical evidence thus far provided, though providing plausible explanations, are of the inferential or empirical weight necessary to come to any conclusions that could be said to be imbued with any clear degree of certitude.
The critics have a serious problem: a really large body of missing data over against their speculative theoretical reconstructions of possible historical phenomena that were not, at the time, clearly and carefully recorded. LDS would like those missing rolls and "books", while critics would prefer the eyewitness references to them had never been written.
The plot thickens...