Walter Brown Gibson's solitaire book?
Has the 150 Solitaire Games book by Walter Brown Gibson been looked into as a source of solitaire games? Looking at the table of contents from https://archive.org/details/150solitairegame00barn/page/n5/mode/2up on the Internet Archive, it seems that most of the games are already in PGS, but it may be worth looking into if it hasn't.
I can't answer for Thomas, except to say that the Internet Archive seems to have something confused here.
Both of these books, The Key to Solitaire (1966) and 150 Solitaire Games (1972 reprint, albeit with a different cover) are in my collection and they are (it was) written by Douglas Brown.
Walter B. Gibson is (to my knowledge) a different person altogether, author of Hoyle's Modern Encyclopedia of Card Games (1974), which lists about 42 types of solitaire under the "Solitaire" entry, though several of these are just alternative names for other solitaire games. (Incidentally, this book includes a list of other works by the author, which does not include either of the above books, both published earlier, but it does include one simply called Solitaire which is not in my collection, so I must track it down. 😉)
I do know that Thomas has a collection of solitaire books and, for various reasons, not every game in those books is implemented.
Clarification: I just realized that reason for the different cover for 150 Solitaire Games is that I have a 1985 reprint of the 1972 version, which was a reprint of The Key to Solitaire. 🙃