According to John Tvedtnes, in recent years, LDS scholars have been struck by some aspects of internal consistency in the Book of Mormon. Lengthy phrases and lists found in early parts of the book are repeated verbatim or nearly verbatim in later sections. For Joseph Smith to have remembered these long after he first dictated them to his scribe is an unreasonable expectation. It would have been much easier for Mormon to have quoted from earlier, written texts in his possession. Consequently, such passages can be seen as evidence that Joseph, too, worked from an extant text.
A FARMS Update ("Textual Consistency," October 1987, reprinted in John W. Welch, ed., Reexploring the Book of Mormon) noted several further instances of textual consistency in the Book of Mormon. One example concerns the precise details of destructions which would take place at the crucifixion of the Savior which had been given by the ancient prophet Zenos in 1 Nephi 19:11-12:
For thus spake the prophet: The Lord God surely shall visit all the house of Israel at that day, some with his voice, because of their righteousness, unto their great joy and salvation, and others with the thunderings and the lightnings of his power, by tempest, by fire, and by smoke, and vapor of darkness, and by the opening of the earth, and by mountains which shall be carried up.
And all these things must surely come, saith the prophet Zenos. And the rocks of the earth must rend; and because of the groanings of the earth, many of the kings of the isles of the sea shall be wrought upon by the Spirit of God, to exclaim; The God of nature suffers.
Each of the cataclysmic events he listed was included in the account of these destructions given in 3 Nephi 8:6-23. [John A. Tvedtnes, "Mormon As an Abridger of Ancient Records," in The Most Correct Book, pp. 17-18]
“Terrible Tempest”
According to Ammon O'Brien, in the course of Brasseur de Bourbourg's researches into the ancient history of Mexico, he found the echoes of some catastrophic event in former times to be quite persistent, abundant and profound. His observations on this topic are based in part on what he found in the contents of Codex Chimalpopoca. Part of that codex was dubbed Legend of the Suns by Professor Francisco Paso y Troncoso who in 1903 rendered a Spanish translation of the Nahuatl text. . . .
The Legends of the Suns designates 676 years as the duration of the first age or epoch, whose catastrophic end was marked by the destruction of the sun--or the time of the great darkness. This framework is potentially quite significant. In previous chapters we have noted that the historical chronology of the Nephite and Lamanite nations commenced from the time that Lehi and his family left Jerusalem. Furthermore, we have noted that according to the Mormon account, the manifestation of the "new star" and night of no darkness occurred exactly 600 years from the commencement of Nephite chronology (see 3 Nephi 1:1), which was quite significant in view of an identical time-frame given in Codex Fuenleal.
Along this course of reasoning we may also determine that a total of 633 years comprises the period of Nephite-Lamanite history from its beginning to the time of the great destruction when the sun was overruled by a shroud of intense darkness. Hence it is peculiar that Codex Chimalpopoca should assign a figure which is so close to the number of years indicated in the Book of Mormon for this epoch of ancient American history.
The Nephite record by its very nature must be taken as the punctually correct version of these events, thus we may confidently surmise that somewhere along the line, the Mexican calculations of this chronology have picked up an excess of 43 years, giving the native total 676 years, when it should be 633.
We find however that this discrepancy of 43 years has a plausible explanation. It is a well known fact that the Mexican calendar system operated on a 52 year cycle. . . . The Codex Fuenleal stipulates:
There were four groups of years, thirteen each, 52 years in all--this they called an age. When those years were completed it was with great solemnity that they commenced their feasts, and started the count of the four groups of years again, to enter another age.
With this in view, we may now observe that 676 years is a precise multiple of 52. In other words, we have here the sum of thirteen ages in the Mexican system. Turning to the Mormon account which designates this great destruction and period of darkness to have taken place in the 634th year from the beginning of Nephite--Lamanite chronology, we see that this does indeed fall within the thirteenth cycle of 52 years (13th cycle spans the years 625 to 676).
Considering the fact that this catastrophe is perceived as having consummated the end of an age, then according to the ancient calendar order, this would be the close of the 13th age, which if calculated arbitrarily would render a total of 676 years. Hence it would appear that the Mexicans were not aware, or at least neglected to take into account, that the 13th age suffered a premature termination. [Ammon O'Brien, Seeing beyond Today with Ancient America, pp. 346-349]