Here we have an example of a complex prepositional phrase (“of their people and also of the people of the Lamanites”) that has been displaced. The relative clause “which are true”, referring to the records, intervenes between records and the postmodifying conjunctive prepositional phrase headed by of. None of the printed editions have placed any punctuation (such as commas, dashes, or parentheses) around the nonrestrictive relative clause “which are true”. Such punctuation would help the reader process this rather difficult construction. For other examples of displaced prepositional phrases in the text, see the discussion under Mosiah 26:23; also see the more extensive list of examples under displaced prepositional phrases in volume 3.
Summary: Use punctuation to show that the nonrestrictive relative clause “which are true” intervenes between records and the postmodifying “of their people and also of the people of the Lamanites”.