Upon the loss of the 116 pages containing the Book of Lehi, Joseph Smith turned to the small plates of Nephi for this period of history. This translation concludes with the Book of Omni and his brief description of Mosiah’s move to the land of Zarahemla.
This is followed by the Words of Mormon. This section was apparently written in preparation for his transfer of the plates to Moroni.
And now I, Mormon, being about to deliver up the record which I have been making into the hands of my son Moroni, behold I have witnessed almost all the destruction of my people, the Nephites.
The plates given to Joseph included the small plates of Nephi used to replace the book Lehi and were uniform in size and appearance to the balance of the plates. In an attempt to rationalize this fact, Gardner has proposed that Mormon used the size of the Brass Plates as a model to make the plates used in Mormon’s abridgment of the Nephite record. We have , however, no description of the Brass Plates so this is pure conjecture.
On the other hand we do have a description of the plates given to Joseph and they included the small plates of Nephi. I would suggest that rather than using the Brass Plates as a model that Mormon used the small plates of Mormon as his model and made sufficient plates at this time to contain his entire projected project. Gardner makes a good case for the proposal that Mormon planned the contents of his plates before he ever engraved anything on the actual plates. It is reasonable that when he went looking for more records after creating the Book of Lehi and found the small plates that he had not yet engraved the Book of Lehi on any plates but rather on some other more easily used medium.If this is true it would account for the uniformity of the plates and preclude the necessity of copying the small plates to those given to Moroni. It would also account for the fact that the book of Mosiah is actually introduced in the last few verses of the Words of Mormon. There is speculation that Joseph had translated the first part of Mosiah and this was lost with the 116 pages. However if one removes the verse numbers and joins the last part of the Words of Mormon to the first part of Mosiah, one gets the following narrative:
And now, concerning this king Benjamin—he had somewhat of contentions among his own people. And it came to pass also that the armies of the Lamanites came down out of the land of Nephi, to battle against his people. But behold, king Benjamin gathered together his armies, and he did stand against them; and he did fight with the strength of his own arm, with the sword of Laban. And in the strength of the Lord they did contend against their enemies, until they had slain many thousands of the Lamanites. And it came to pass that they did contend against the Lamanites until they had driven them out of all the lands of their inheritance.
And it came to pass that after there had been false Christs, and their mouths had been shut, and they punished according to their crimes; And after there had been false prophets, and false preachers and teachers among the people, and all these having been punished according to their crimes; and after there having been much contention and many dissensions away unto the Lamanites, behold, it came to pass that king Benjamin, with the assistance of the holy prophets who were among his people— For behold, king Benjamin was a holy man, and he did reign over his people in righteousness; and there were many holy men in the land, and they did speak the word of God with power and with authority; and they did use much sharpness because of the stiffneckedness of the people— Wherefore, with the help of these, king Benjamin, by laboring with all the might of his body and the faculty of his whole soul, and also the prophets, did once more establish peace in the land.
*And now there was no more contention in all the land of Zarahemla, among all the people who belonged to king Benjamin, so that king Benjamin had continual peace all the remainder of his days. And it came to pass that he had three sons; and he called their names Mosiah, and Helorum, and Helaman. And he caused that they should be taught in all the language of his fathers, that thereby they might become men of understanding; and that they might know concerning the prophecies which had been spoken by the mouths of their fathers, which were delivered them by the hand of the Lord.
And he also taught them concerning the records which were engraven on the plates of brass, saying: My sons, I would that ye should remember that were it not for these plates, which contain these records and these commandments, we must have suffered in ignorance, even at this present time, not knowing the mysteries of God. For it were not possible that our father, Lehi, could have remembered all these things, to have taught them to his children, except it were for the help of these plates; for he having been taught in the language of the Egyptians therefore he could read these engravings, and teach them to his children, that thereby they could teach them to their children, and so fulfilling the commandments of God, even down to this present time. I say unto you, my sons, were it not for these things, which have been kept and preserved by the hand of God, that we might read and understand of his mysteries, and have his commandments always before our eyes, that even our fathers would have dwindled in unbelief, and we should have been like unto our brethren, the Lamanites, who know nothing concerning these things, or even do not believe them when they are taught them, because of the traditions of their fathers, which are not correct.
O my sons, I would that ye should remember that these sayings are true, and also that these records are true. And behold, also the plates of Nephi, which contain the records and the sayings of our fathers from the time they left Jerusalem until now, and they are true; and we can know of their surety because we have them before our eyes. And now, my sons, I would that ye should remember to search them diligently, that ye may profit thereby; and I would that ye should keep the commandments of God, that ye may prosper in the land according to the promises which the Lord made unto our fathers. And many more things did king Benjamin teach his sons, which are not written in this book.
This reads to me as though it should be read together and the part from The Words of Mormon is the missing introduction to Mosiah and any information about Mosiah lost in the 116 pages was actually part of the Book of Lehi. The * designates the point where the two parts are divided in the present text of the Book of Mormon.