13 Now Ammon said unto him: I can assuredly tell thee, O king, of a man that can translate the records; for he has wherewith that he can look, and translate all records that are of ancient date; and it is a gift from God. And the things are called interpreters, and no man can look in them except he be commanded, lest he should look for that he ought not and he should perish. And whosoever is commanded to look in them, the same is called seer.In Mosiah 28:11-17, 20 chapters later, we find out that King Mosiah (near the end of his life) translates the records. A summary of the translation of these records becomes the Book of Ether (compiled by Moroni). They are referred to several times prior to that, perhaps most notably in Alma 37 (see verse 21 for example).
14 And behold, the king of the people who are in the land of Zarahemla is the man that is commanded to do these things, and who has this high gift from God.
In fact, an editorial promise to give an account of this record is found in verse 19:
19 And this account shall be written hereafter; for behold, it is expedient that all people should know the things which are written in this account.Thus, the author of the book needs to remember to include this record in order to fulfill this promise. There are dozens of editorial promises in the Book of Mormon. The author of this book clearly had a lot of time and a lot of notes.