Isaiah 51:21 (King James Bible) thou afflicted and drunken but not with wine
Here the Book of Mormon text has and instead of the but of the King James Bible. As already noted in the discussion regarding strait versus straight in 1 Nephi 8:20, there has been considerable shifting between and and but in the Book of Mormon manuscripts as well as editions. So it is possible that here in 2 Nephi 8:21 we have an error, but it is equally possible that the change is intended. In this instance, either conjunction will work. The safest recourse, then, is to follow the earliest textual sources in determining whether the Book of Mormon text should read and or but. This same procedure will also be followed in the numerous cases where there is either an omitted or an added conjunction in the Book of Mormon text. Unless there is some variation within the history of the Book of Mormon text itself or some difficulty with the reading itself, such cases will not be discussed in this volume. For an example that does involve manuscript variance, see 2 Nephi 15:7.
Summary: Maintain the conjunction and in 2 Nephi 8:21, even though the corresponding Isaiah verse has but; in general, we assume that the conjunction found in the earliest textual sources for the Book of Mormon is intended unless there is some specific evidence for an error; simply finding a difference with the corresponding King James text is insufficient reason to emend the Book of Mormon text.