According to danhausser's site, "Mission To Horatius" is considered a Bantam book...
That's not true. The site is named "Guide to the Early STAR TREK Novels," not "Guide to the Bantam STAR TREK Novels." And the entry for Mission to Horatius
explicitly says "Published in 1968 by Whitman Books," while all the others listed on the page say "Published in [date] by Bantam Books." And at the bottom of the page is a copyright disclaimer reading in part, "The above mentioned books were published by Bantam Books
, and by the Whitman
Publishing Division of Western Publishing Company, Inc."
Granted, the home page does have a sentence saying "This site is a guide to those early STAR TREK
novels published by Bantam Books," but that's probably an uncorrected bit of text from the early edition of the site before MtH was reprinted by Pocket, or maybe just an error. Everything else on the site makes it quite clear that MtH was a Whitman book, not a Bantam book.