I haven't seen any edition of These Are the Voyages but would like to note that major publishers (allegedly with professional editors on staff) also have been known to produce supposedly well-researched books that turn out to have problems just as large as those reported here.
Case in point: I recently read last year's biography of Kurt Vonnegut Jr. by Charles Shields, published by Henry Holt. Despite hundreds of endnotes, there are some serious problems that anyone moderately knowledgeable about Vonnegut's career would have been aware of.
One major piece of missing information involves the 1974 novel by "Kilgore Trout," Venus on the Half-Shell (first published as a serial in F&SF). Shields fails to mention that the title and a short excerpt from it (reused by the actual author, Philip Jose Farmer) first appeared, along with Trout himself, in Vonnegut's 1965 novel God Bless You, Mr. Rosewater. Because Vonnegut is depicted as remorseful that he'd given permission to Farmer to write the novel, it's obviously pertinent that Vonnegut himself had planted the seed for it.
There are also some unsupported assertions. One that I recall (checked Amazon just now for the quote) is "the publisher made the mistake of leaving off 'Jr.' after his surname on the cover" with regard to the 1976 novel Slapstick, as if "Jr." had appeared anywhere else in the book - which it didn't! (Yes, I have the hardcover, and yes, I can see why it got bad reviews at the time.) Vonnegut's final book to use the "Jr." was Breakfast of Champions 3 years earlier, and despite Shields' assertion there is no reason to think a mistake was involved.
And so on.