Again, this statement indicates that Mormon has not yet abridged the record from Mosiah to Mormon. He has only accomplished the work to the reign of Benjamin.
"The Words of Mormon were apparently written near the end of Mormon's life for the purpose of connecting two major records. It was made known to Mormon 'by the workings of the Spirit of the Lord' that the small plates of Nephi (which ended when Benjamin was a relatively young man) might be used to replace his abridgment of the book of Lehi (which ended when Benjamin was an old man about ready to die). So that a gap would not occur in the history of the Nephites, Mormon included the major events of the lifetime of King Benjamin in The Words of Mormon, thus connecting the account on the small plates of Nephi with Mormon's abridgment of the book of Mosiah." (Daniel Ludlow, A Companion to Your Study of the Book of Mormon, p.171)