Here in both manuscripts, Oliver Cowdery initially omitted the of that heads the relative clause. In each case, he supralinearly inserted the of and without any change in the level of ink flow. For the case in 𝓞, Oliver initially wrote a t, then crossed it out and supralinearly inserted the of. Perhaps he started to write that instead of which or to rewrite the preceding those. The supralinear of in 𝓞 appears to be an immediate correction. Obviously, Oliver tended to omit the initial of that headed this relative clause.
An almost identical example of this tendency to omit the initial of is found a few verses later in this chapter—and again in both manuscripts:
In this instance, the corrected of in 𝓞 was written with somewhat heavier ink flow, but for the corrected of in 𝓟 there is no difference in the level of ink flow. Thus in this second instance, the correction in 𝓞 may have occurred later, perhaps when Oliver read back the text to Joseph Smith, or perhaps much later, when Oliver copied the text from 𝓞 into 𝓟. This correction in verse 24 is, in any event, in agreement with the invariant placement of the of at the beginning of an almost identical relative clause that occurs two verses earlier in the text:
One could argue that Oliver’s correction in verse 24 was a conscious one based on the reading in verse 22.
As noted under 1 Nephi 10:16, the Book of Mormon text prefers of at the head of relative clauses when the verb is speak. More specifically, when we have the passive form spoken, we get a more evenly divided distribution for the placement of the of; I include in the following list the two cases here in Alma 40 where the of was initially omitted (each marked below with an asterisk):
at the beginning of the relative clause (13 occurrences)
after the verb phrase in the relative clause (9 times)
We note the strong tendency in these relative clauses to place the of after spoken when there is a following prepositional phrase (usually an agentive by-phrase) as well as the opposite tendency to place the of at the beginning of the relative clause when spoken is not followed by any prepositional phrase. But since there are exceptions to both tendencies (namely, Mosiah 4:8, Alma 5:21, and Alma 40:22, 24), we allow in each case the earliest textual sources to determine the placement of the of. Even if the insertion of the of in verse 24 is due to later editing on Oliver Cowdery’s part, it was likely correct given the placement of the of in verse 22 (which reads almost identically).
David Calabro points out (personal communication) that the of may have originally been lacking in Alma 40:24 since the language there parallels the language of the King James Bible— and the biblical text lacks the initial of:
However, the parallel language is actually not that close: in the biblical text, we get restitution rather than restoration, the use of the active rather than the passive in the relative clause, the singular mouth rather than the plural mouths, and the more complex noun phrase, “all his holy prophets since the world began”, rather than the simpler “the prophets”. If the issue is parallelism, then Alma 40:24 is closer to Alma 40:22, and in that instance the of is the firm reading in both manuscripts (repeated here for convenience):
There would be no reason to omit the simple function word of in verse 24 but leave it in verse 22.
And finally, we should note that there is firm evidence that Oliver Cowdery had difficulty elsewhere in the manuscripts with writing down the initial of at the head of relative clauses, including other cases where the verb was speak:
For both of these cases, Oliver initially omitted the of in 𝓟. For two possible cases where he appears to have failed to supply the of in 𝓟, see the discussion under Alma 13:14 and Helaman 16:16.
Summary: Accept in Alma 40:19 and in Alma 40:24 the of at the beginning of the relative clauses “of which have been spoken” and “of which has been spoken by the mouths of the prophets”; the reading in verse 24 is supported by the virtually identical but invariant language in verse 22: “of which have been spoken by the mouths of the prophets”; the reading in verse 19, with of at the beginning of the relative clause, is strongly supported by usage elsewhere in the text.