The 1837 edition introduced first in front of “chief judge”. Joseph Smith did not mark this change in the printer’s manuscript, yet the change does appear to be a conscious one and could well be Joseph’s. Since 𝓟 does not have the first, the 1908 RLDS edition removed it from the RLDS text. It is very doubtful that the original manuscript was the source for Joseph supplying the first in the 1837 edition since there is no specific evidence that he ever used the original manuscript in his editing for that edition. It appears that the source for adding the ordinal first was the occurrence of “the first and chief judge” nearby in verse 44 and twice in the preface to the book of Alma (which immediately follows verse 47):
The phrase “first chief judge” occurs nowhere else in the text. So if the 1837 change in verse 42 is accepted in the standard text (but not in the critical text), perhaps it should be emended from “first chief judge” to “first and chief judge”, at least to be more consistent with the three nearby examples.
The use of the and in “the first and chief judge” does appear to be intentional, especially since it occurs three times at the transition between the books of Mosiah and Alma. We also find a similar use of and in the original text for another example involving a conjoined adjective (in this instance, great rather than first):
Despite these examples, there is an occurrence of “second chief judge” in the text, which clearly implies that “first chief judge” is possible:
Everywhere else, however, the text refers simply to the “chief judge” without a preceding ordinal; some of these occurrences refer to the chief judge over all the Nephites (as in Alma 4:17 and Alma 27:20) and others to the chief judge over a particular land (as in Alma 14:4 and Alma 30:21). In none of these examples is there any reference to a first or second chief judge. Consequently, there is no crucial need to have added first in Mosiah 29:42.
These examples with the preceding ordinal number seem to be using first and second in the sense of sequencing in time. There appears to be no use of first with judge in the sense of ‘supreme’ or ‘highest’. Instead, the word chief seems to take on this role in the text.
Summary: Delete the intrusive first from Mosiah 29:42 since it was not there originally, nor is it necessary; the intrusive first, if maintained in the standard published text, should perhaps read “first and chief judge” to make the text consistent with the three nearby occurrences of “first and chief judge”.