We’re studying the Book of Mormon again in seminary, and the current manual includes the following quotation from Joseph Fielding Smith (Lesson 5, “Overview of the Book of Mormon”):
There were bound to be some typographical errors in the first edition [of the Book of Mormon], and perhaps an omission of a word or two. Those who have published books under the most careful and favorable circumstances, have, to their dismay, found errors, typographical and mechanical, some of which occurred after the final examination of proof has been made.
… A careful check of the list of changes … shows there is not one change or addition that is not in full harmony with the original text. Changes have been made in punctuation and a few other minor matters that needed correction, but never has any alteration or addition changed a single original thought. As it appears to us, the changes … are such that make the text clearer and indicate that they were omitted. I am sure that the mistakes or omissions in the first edition were in large measure the fault of the compositor or the printer. Many of these mistakes which were in the first proofs were caught by the Prophet Joseph Smith himself, and he made the corrections (Joseph Fielding Smith, Answers to Gospel Questions, comp. Joseph Fielding Smith Jr. , 2:199–200; italics in original).
The problem is that the second paragraph is almost entirely false. We can now compare the extant original manuscript and printer’s manuscript with the 1830 edition, and there are indeed several changes that make a difference in meaning, that modified more than “a single original thought.” Not all the changes made the text clearer. Joseph Smith did not catch many mistakes since he was living elsewhere and rarely interacted with the printer. And most importantly, mistakes and omissions are not to be blamed on the compositor or the printer.