In his editing of 𝓟 for the 1837 edition, Joseph Smith deleted which were here in Alma 23:5, thus creating a postmodifying past-participial phrase (“the records and the prophecies handed down even to the present time”). The resulting construction, it turns out, is not characteristic of the Book of Mormon text; thus it is appropriate that this emendation was not implemented in the 1837 edition.
Elsewhere in the text there are other cases where nouns (namely, records, prophecies, tradition, and oaths) are followed by handed down, and in each instance handed down is found in a relative clause rather than as a postmodifying past-participial phrase. In each case (listed below), the part in bold could be lacking but is not:
(Of course, in the last example, it would be difficult to omit the “which had been” given the preceding parenthetical relative clause, “which was given by them of old who also sought power”.) Clearly, the original text in Alma 23:5 is the expected expression and will be retained in the critical text.
Summary: In Alma 23:5 Joseph Smith’s crossout in 𝓟 of which were was never implemented in the 1837 edition; the original reading is definitely correct since the Book of Mormon text consistently prefers the relative clause form over the past-participial form for the postmodifying passive phrase handed down.