The 1830 typesetter accidentally deleted the repeated the in the phrase “the Nephites and the Lamanites”. In accord with the reading of the printer’s manuscript, the 1908 RLDS edition restored the repeated the to the RLDS text. Elsewhere in the Book of Mormon, there are no other cases of “the Nephites and Lamanites” (the common phraseology in modern English), only the fuller “the Nephites and the Lamanites” (13 times). Similarly for the opposite order, we have only “the Lamanites and the Nephites” (3 times). Thus the original text was perfectly consistent for this particular conjunctive phrase. For further discussion, see conjunctive repetition in volume 3.
In modern English, of course, we do not normally repeat the definite article the in conjunctive phrases, thus the tendency to occasionally omit the repeated the. Besides this accidental omission in the 1830 edition, the 1840 edition has two similar losses of the repeated the in conjuncts involving “the Nephites” and “the Lamanites”:
Summary: Restore in Enos 1:24 the definite article the before Lamanites (the reading in the printer’s manuscript); the original text consistently reads “the Nephites and the Lamanites”, never “the Nephites and Lamanites” (the phraseology that we expect in modern English).