Question: How does the spelling of Coriantumr, a dissenter from the Nephites and leader of the Lamanite military, show that Joseph Smith spelled out proper names as he translated the plates?
Answer: Scribal corrections in the original Book of Mormon manuscript show that Joseph Smith spelled out unfamiliar names as he translated the plates. For example, scribe Oliver Cowdery first spelled Coriantumr as Coriantummer. He crossed out the name and wrote in its place Coriantumr.
As Royal Skousen wrote, “This name could not have been spelled correctly unless Joseph Smith spelled it out letter by letter. In fact, Oliver ended the final ‘r’ of the correct spelling with a huge flourish of his quill, almost as if to say, ‘How could anybody be expected to spell such a name?’”
“Therefore he did stir them up to anger, and he did gather together his armies, and he did appoint Coriantumr to be their leader...” (Helaman 1:17)
Source: 400 Questions and Answers About the Book of Mormon by Susan Easton Black, p. 168.