In discussing examples of passages from Isaiah which appear to be copied from the King James Bible into the Book of Mormon, scholars have found variations in the text. Jeff Lindsay notes that this issue of Isaiah variants in the Book of Mormon is actually fairly complex and interesting. Lindsay includes a quote from Franklin Harris discussing one example:
To Isaiah 29:21 the Book of Mormon in 2 Nephi 27:32 adds the phrase "and they" to the beginning of the verse. The Septuagint and Syriac both read the same as the Book of Mormon. (Franklin S. Harris, Jr., The Book of Mormon: Messages and Evidences, pp. 50-52)
[Quoted by Jeff Lindsay, "Did Joseph Smith Plagiarize from the King James Bible?," Book of Mormon Commentary, [www.jefflindsay.com]]