As explained under the Words of Mormon 1:14, we get many thousand only when it premodifies a semantically plural noun, as in Alma 28:10: “many thousand lives”. When there is a postmodifying prepositional phrase, the text always has many thousands, as in Alma 28:12: “many thousands of others”. In a few instances, there has been a tendency to replace “many thousands of X” with “many thousand of X”. Such an error initially occurred in the Words of Mormon 1:14 when Oliver Cowdery copied the text from 𝓞 into 𝓟. Here in Alma 26:13, the 1953 RLDS edition made the same error. The 1953 change was probably not intentional since for all other instances of “many thousands of X” (six of them) the 1953 edition retained the original thousands. One further example of this error occurred in the 1830 edition:
In this instance, the 1837 edition restored the correct thousands; see the discussion under Alma 37:9.
Summary: Maintain the correct plural expression “many thousands of X” in Alma 26:13 and elsewhere in the text.