Here the word all was omitted in the 1840 edition, probably accidentally. The 1908 RLDS edition restored the word to the RLDS text; the LDS text, since it derives from the 1837 edition but not the 1840 edition, has maintained the original all. The 1840 edition has this same typo in Helaman 14:7. As explained under that passage, the typesetter’s eye seems to have skipped the all because the immediately preceding shall ends in all.
Summary: Maintain the word all in 3 Nephi 29:2: “the words of the Lord … shall all be fulfilled”.