Here the 1892 RLDS edition replaced the plural have with the biblically styled hath. As explained under the phrase “Nephi’s brethren rebelleth” in the 1 Nephi preface, plural subjects frequently take the historical third person singular ending -(e)th in the original text of the Book of Mormon. This example in the 1892 edition shows the opposite tendency, namely, of replacing the standard have with the biblical hath for the plural antecedent books. The 1908 RLDS edition restored the correct have to the RLDS text.
Summary: Maintain the plural verb form have in 3 Nephi 27:25 (“out of the books which have been written”); the accidental use of hath in the 1892 RLDS edition would have been possible in the original text, although not required.