Here is the second clear example of Joseph Smith using the original manuscript to restore a phrase (“for all men”) that had been accidentally skipped when Oliver Cowdery copied from 𝓞 into 𝓟. Joseph used 𝓞 to correct the text for only the 1840 edition. The 1841 British edition was set from the 1837 edition; thus the 1841 edition and the subsequent 1849 British edition are missing the phrase. The first printing of the 1852 British edition also lacks the phrase, but for the second printing of that edition, the 1840 edition was consulted (at least for this part of the text) and the phrase was thus restored to the LDS text. The more recent RLDS text does not have the phrase since the 1908 edition was based on the printer’s manuscript.
The loss of the phrase “for all men” is quite natural. Elsewhere the text does not explicitly state that the way is prepared for all; the universal applicability of the way is either assumed or otherwise explained:
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Summary: Maintain in 1 Nephi 10:18 the phrase “for all men” since it is found in 𝓞; this short phrase was accidentally lost when Oliver Cowdery copied from 𝓞 into 𝓟.