“The early history contained in the Book of Mormon is obtained from three sets of plates: the brass plates of Laban, the small plates of Nephi, and the large plates of Nephi. However, when Limhi’s people join with the people of King Mosiah in the land of Zarahemla they bring with them two additional sets of plates: (1) their own records, which are known as the record of Zeniff, and (2) the ‘records which had been found by the people of Limhi,’ which are later identified as the records of Ether. (See Ether 1:1–2)” (Ludlow, Companion to Your Study of the Book of Mormon, 188).
The superscription to Mosiah 23 was part of the ancient record translated by the Prophet Joseph Smith and dictated by him to his scribe.
The phrase in italics below the superscript is not from the ancient record but was added later to clarify which chapters in the book of Mosiah constitute the account of Alma in the land of Helam.