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Source:Rediscovering the Book of Mormon:Ch:4:5:Colophons: Helaman
The book of Helaman begins with a lengthy preface stating that it is a record of Helaman (II), who was son of Helaman (I), and of the sons of Helaman (II). The same statement is found in Helaman 16:25. In 3:37, Mormon noted the passing of Helaman II, whom his son Nephi succeeded as judge.
A preface before chapter seven tells us that Nephi wrote the chapters of the book of Helaman after that point. Helaman 7-12 has a formal title, "The prophecy of Nephi, the son of Helaman," as well as a preface mentioning the prophecy of Samuel, which begins with chapter thirteen. The preface leads me to think that this material was an extract from a separate record in Mormon's possession. Clearly a number of men had a significant hand in producing the book of Helaman. What is not clear is why the "books" were not divided up and labeled some other way, for example, turning the single book we know as Helaman into "Helaman II," "Nephi, son of Helaman," and "Lehi, son of Helaman."...Considering the way Joseph dictated the book to scribes, for the most part in a matter of weeks without revising what he had dictated, we should realize that he could not himself have come up with this complicated set of prefaces and summaries. It is unlikely that he would go to the trouble to insert anything like them (they are not required to move the story along). It is also most unlikely that, while dictating, he could keep in mind what he had promised in the prefaces and then remember to close off so many sections neatly with summaries. Much more believable are the claims in the Book of Mormon itself that the record was done by ancient writers working with written materials over long periods of time.