Here we have two instances where the original manuscript has the cardinal number six rather than the expected ordinal number sixth. A third instance is found later in this chapter:
In these three verses, Oliver Cowdery emended the six to the expected sixth when he copied the text from 𝓞 into 𝓟. There are no other instances in the text where we get six instead of the expected sixth; out of 22 other instances of sixth (of which seven are extant in 𝓞), we get an invariant sixth.
These three occurrences of six in place of sixth appear to be the result of the tendency in continuous speech to simplify a complex consonant cluster—in this instance, to omit the voiceless interdental fricative /h/ when preceded by the obstruent cluster /ks/ at the end of six and followed by a consonant (namely, the initial y of year). Under these phonetic conditions, it takes some articulatory effort to maintain the /h/ in sixth year. Here in Alma 56, Joseph Smith could have pronounced sixth as simply six, with the result that Oliver Cowdery wrote down six instead of sixth three times in 𝓞.
David Calabro (personal communication) has suggested one alternative that needs to be considered: namely, the original text here in Alma 56 may have actually read “twenty and six year” in all three of these cases. As discussed under Alma 52:15, we expect the last number (and only the last number) in a compound ordinal to take the ordinal form (as in “twenty and sixth year”). Nonetheless, there are examples in Early Modern English where the last number in a compound ordinal number was actually a cardinal, as in the following examples from Literature Online:
Although there are no examples listed on Literature Online involving six, such examples were undoubtedly possible. The cases involving one and two clearly show that the issue here is not a phonetic one since the expected ordinal forms, first and second, are so different from their cardinal forms. In other words, there really seems to have been a tendency in Early Modern English, although not especially frequent, to make the last number in a compound ordinal a cardinal number. But in the Book of Mormon, we find no independent evidence that the occurrence of six instead of sixth in Alma 56 is due to this kind of tendency. There are, for instance, no examples of compound ordinals, even as mistakes, where first is replaced by one or second by two. The only instances in 𝓞 of the cardinal in place of the ordinal are the three examples of six here in Alma 56 and one example of eight later on in the book of Helaman:
But there is independent evidence that the difficulty here with eighth is orthographic, not phonetic. For discussion of that evidence, see under Helaman 3:19.
The critical text will assume that the three instances in 𝓞 of six in “twenty and six year” is the result of Joseph Smith omitting the /h/ sound in his pronunciation of sixth year, which led Oliver Cowdery to write down six rather than the correct sixth three times in 𝓞. Thus Oliver’s later decision to consistently emend “twenty and six year” to “twenty and sixth year” was undoubtedly correct.
Summary: Accept in Alma 56:7, 9, 20 Oliver Cowdery’s emendation in 𝓟 of six to sixth in the phrase “twenty and six(th) year”; the omission in 𝓞 of the /h/ sound in Oliver’s spellings of sixth was most probably the result of Joseph Smith’s pronunciation of sixth year as six year.