Isaiah 52:15 (King James Bible) so shall he sprinkle many nations the kings shall shut their mouths at him for that which had not been told them shall they see and that which they had not heard shall they consider
We have two cases of textual variation in 3 Nephi 20:45. First, the earliest textual sources are missing the negative not in the first of two parallel clauses (thus “for that which had been told them”), which means that either Joseph Smith or the scribe in 𝓞 (presumably Oliver Cowdery) omitted the not during the dictation of the text. This not was supplied in the 1879 LDS edition (and in the 1953 RLDS edition). Most probably, the original manuscript lacked the not since both the printer’s manuscript and the 1830 edition are missing the not. But the missing not in 𝓞 would have been an accident since (1) both not ’s occur in the corresponding King James text (in Isaiah 52:15), and
(2) both not ’s occur in the next chapter of 3 Nephi, which also quotes the King James version of Isaiah 52:15:
Thus the 1879 and 1953 emendation that supplied the not is very likely the original reading of the Book of Mormon text for 3 Nephi 20:45. For another case where Oliver permanently omitted a not from the text (in this other case, when he copied from 𝓞 into 𝓟), see under 1 Nephi 12:5. There are also a number of cases where Oliver momentarily omitted the not in 𝓟:
The other textual variant here in 3 Nephi 20:45 is the word order “they shall see” that the 1905 LDS edition introduced into the LDS text. The 1920 LDS edition restored the original (and correct) inverted word order (“shall they see”). Once more, Isaiah 52:15 and 3 Nephi 21:8 each have two parallel occurrences of the inverted word order (just as 3 Nephi 20:45 did originally):
Summary: Accept the 1879 LDS emendation of 3 Nephi 20:45 with the inserted not because of the otherwise identical quotation of Isaiah 52:15 in 3 Nephi 21:8; similarly, the original inverted word order “shall they see” should be maintained in 3 Nephi 20:45 (as well as in 3 Nephi 21:8).