Isaiah 48:21 (King James Bible)
he caused the waters to flow out of the rock for them he clave the rock also and the waters gushed out
The past-tense form clave was probably what Joseph Smith originally saw, but because of the rarity of this past-tense form and its lack of an overt sign of the past tense, the past-tense marker -d was accidentally added, perhaps by Joseph Smith as he read off the text or by Oliver Cowdery as he wrote down Joseph’s dictation. It is also possible, as David Calabro points out (personal communication), that the following the (which begins with a voiced interdental fricative) would have made it easy for Oliver to have misinterpreted /kleiv dß/ as having a /d/ at the end of clave; that is, he misheard /kleiv dß/ as /kleivd dß/ and thus wrote down “claved the rock”. For a similar kind of misinterpretation, see the discussion regarding the phrase “as we supposed that” in Alma 56:37.
At some later time, this extra d in claved was crossed out in the original manuscript with heavier ink flow. It is quite possible that this deletion occurred even after the printer’s manuscript was copied since that manuscript (namely, 𝓟) reads cleaved, a regularization of the past tense that is more easily derived from the spelling “claved” than from “clave”. This same regularized past-tense form cleaved is found in the 1830 edition. In his editing of 𝓟 for the 1837 edition, Joseph Smith crossed out the final d of cleaved (as well as the e right before the d ), but he neglected to cross out the first e in cleaved. In any event, the 1837 typesetter interpreted Joseph’s correction as clave (not cleave, which would not have made sense). The archaic (but textually correct) pasttense clave has been the reading in the Book of Mormon text ever since.
There are no other occurrences of the simple past-tense clave in the Book of Mormon. There are eight occurrences of the verb cleave, of which two use the auxiliary do to form the past tense (namely, “did cleave” in 3 Nephi 10:10 and Ether 14:2).
Summary: Maintain the archaic past-tense form clave in 1 Nephi 20:21, the corrected reading in 𝓞 and the reading in the King James Bible.