Redaction: When Amaleki delivers the plates to king Benjamin, Benjamin "took them and put them with the other plates, which contained records which had been handed down by the kings…" As has been suggested, the "plates of Nephi" became the traditional record of the kings, and as such, would have preserved in their titles the names of each king. This not only suggests the nature of the dual line of transmission for the large and small plates of Nephi, but also suggests one other possibility.
In the preface to the 1830 edition of the Book of Mormon, Joseph Smith indicates: "I would inform you that I translated, by the gift and power of God, and caused to be written, one hundred and sixteen pages, the which I took form the Book of Lehi, which was an account abridged from the plates of Lehi, by the hand of Mormon…" (Preface, Book of Mormon. 1830 facsimile edition, Herald Heritage Reprint. 1970.) The preface was removed in the 1837 and subsequent editions of the Book of Mormon (Brewster, Quinn. "The Structure of the Book of Mormon: A Theory of Evolutionary Development." Dialogue. P. 130).
Brewster's analysis of the structure of the Book of Mormon suggests that Joseph Smith was not completely cognizant of the interrelationships among the source plates as he was dictating the text. (Brewster, Quinn. "The Structure of the Book of Mormon: A Theory of Evolutionary Development." Dialogue). While his analysis depends upon a very different reading of the hints in Words of Mormon (for instance, Brewster sees Mormon writing the Mosiah-Mormon section after Words of Mormon. See p. 132) he is apparently correct that Joseph did not have an accurate understanding of the composition of the plates. The best evidence is the preface's indication that the Book of Lehi was taken from the plates of Lehi. This is not correct, according to the internal evidence from the translation we have received.
What is undisputed is that the lost 116 pages constituted a "Book of Lehi." Nevertheless, the translation that picks up immediately in Mosiah comes from the plates of Nephi, according to the consistent references Mormon makes in the Mosiah-Mormon section of our current Book of Mormon.
It is also certain that there was a record of Lehi's deeds, probably created early in the family exodus, which served as a resource for Nephi's citations of Lehi in Nephi's record that we have in 1 and 2 Nephi (see Brown, S. Kent " Nephi's Use of Lehi's Record." In: Rediscovering the Book of Mormon. ed. John L. Sorenson and Melvin J. Thorne. FARMS 1991, pp. 3-14). In spite of the existence of this original record, what we have in our current Book of Mormon is Nephi's abridgement, molded into his own narrative (1 Nephi 1:17).
Our course all this tells us is that there was a record of Lehi, and therefore the possibility that the Book of Lehi came from the "plates of Lehi," just as Joseph said in the 1830 preface. However, the evidence from 2 Nephi seems to counter that proposal, as well as the probably nature of Lehi's record. Brown suggests that Lehi's account was likely begun while yet in Jerusalem, and was continued throughout the family exodus. The necessity of carrying the record when they already had the heavy brass plates suggests that it was probably written on a perishable material (see Brown, 1991, p. 5 for his full analysis on the reasons for suspecting a perishable material rather than metal plates).
When Nephi flees from his brothers, he specifically mentions taking the brass plates and the Liahona, but no mention is made of any other plates (2 Nephi 5:12). Later in that same chapter, Nephi speaks of his "other plates" on which he has a more particular history (2 Nephi 5:29). Thus we know that Nephi made an abridgement of the record of Lehi on at least the small plates, and that he made and kept a more complete record on the large plates. While a record of Lehi certainly existed, it does not appear to have existed on metal plates, and our current Book of Mormon is an abridgement of plates, never mentioning perishable sources. Indeed, Jacob specifically notes that perishable records would indeed perish (Jacob 4:1-2).
The suggested resolution to this excursion into the Book of Mormon "plate tectonics" is that Joseph simply assumed plates of Lehi because of the plates and source material, and the existence of the Book of Lehi. The Book of Lehi was an abridgement by Mormon from the "plates of Nephi," or the large plates. When Nephi wrote that set of plates, he was using apparently began with the Book of Lehi, and did not change the book to his own name when he became the ruler (regardless of the nature of the source material of Lehi's record, it is clear that the Book of Lehi as translated continued to the beginning of our Book of Mosiah). It is unknown whether or not there were "book" divisions, but since the 116 manuscript pages are consistently known as the Book of Lehi, it appears that there were no other divisions.
The last interesting question would be why the "unbooked" Book of Lehi - with apparently no "book" divisions for different rulers (though different chapters would be certain) suddenly changed names only at the Benjamin/Mosiah break. The Printer's Manuscript for our Book of Mosiah originally listed it as "Chapter II" rather than "Chapter I" (Book of Mormon Critical Text. FARMS 1987, 2:356). Since the best evidence is that Joseph recommenced his translating with Mosiah rather than 1 Nephi, (see Book of Mormon Critical Text. FARMS 1987, pp. 33-37) this appears to suggest that some of the Book of Mosiah covered the reign of Benjamin. I would suggest that it might have been the book of Mosiah I, and that the break from the ruling dynasty for the city of Nephi was the reason for the shift in the naming convention in our received text. It appears that this possibility of naming the gross "book" for the dynastic founder may also explain the reason that there was no Book of Benjamin. Benjamin certainly reigned during important times, and his farewell speech is a classic, but all we know of Benjamin comes from the sparse notes in Omni and Words of Mormon, and the official inclusion in the Book of Mosiah.