In 1 Nephi 18:15, the earliest text (the original manuscript) has two occurrences of the phrase “much swollen”. The first one, however, is exceptional in that it also has exceedingly (“much swollen exceedingly”), which is highly redundant. Nowhere else in the text do we simultaneously get both the adverbs much and exceedingly modifying the same verbal form. Furthermore, when the adverb much (meaning ‘to a large degree or extent’) modifies a verb phrase, much always follows the verb phrase rather than coming just before the main verb:
On the other hand, when be is the main verb and there is an adjectival past participle, we always get much before the past participle. The following list includes the second occurrence of “much swollen” from 1 Nephi 18:15:
The problem with the first occurrence of “much swollen” in 1 Nephi 18:15 is that, in contradiction to the placement of much, the word swollen is a verb (“they had swollen exceedingly”) rather than an adjective. For this reason, Joseph Smith, in his editing for the 1837 edition, ended up deleting the much. Initially, however, Joseph deleted exceedingly, but then he changed his mind and restored the exceedingly and deleted the much. If he had ended up deleting exceedingly, the resulting “they had much swollen” would have still been wrong since the helping verb was had instead of be. The verb phrase “had swollen” would have required that the much come after the main verb (“they had swollen much”). Of course, another editing alternative is that the perfect auxiliary verb had could have been replaced by were (“they were much swollen”, where they refers to Nephi’s wrists).
All of this evidence suggests that Joseph Smith’s final editing actually represents the original text for this passage—namely, “they had swollen exceedingly”. The original manuscript reads incorrectly, it would seem, because the word much was accidentally inserted before the first swollen under the influence of the following “mine ankles were much swollen”. This error could have easily occurred during dictation. If Joseph Smith had dictated this passage without pausing between the two clauses containing swollen (a dictation sequence of only 13 words, which would have normally been perfectly acceptable), Oliver Cowdery could have readily miswritten the earlier swollen as much swollen since he would have just heard Joseph dictate the later “were much swollen” as he (Oliver) came to write down the first swollen (“they had swollen exceedingly”).
Summary: Accept Joseph Smith’s emendation “they had swollen exceedingly” since this reading probably represents the original text; the original manuscript reads “they had much swollen exceedingly”, an error apparently due to the immediately following clause, “mine ankles were much swollen”.