Nicely centered 67 Mantle, Elm! That's a beauty! And thanks for posting that Trader Speaks ad, Dave! Bob had gotten some of his artwork published in the Sporting News in 65-67 (including one cover!) and was really kicking into his baseball phase of his work by 1967. He had done illustrations for some comic books and magazines in the 50s and 60s, and started dabbling in baseball cartoon artwork, combining his two passions. He started his set in 1967 and was intending to do 63 cards - 1903 -1966. Skipping over the 1904 No Series year, he printed them in sheets of 9 each, so 7 sheets of 9. As you can see by the back of Elm's nice Bob Gibson above, he decided to do a little extension and added in the 1967 card as well, and changed the layout of the bottom of that card to be "No. 64 ... Write for the entire set of 64" All of the other cards still referenced a set of 63. He produced 250-300 sets in total of his 1967 set, distinguished by the second line on the bottom including his address. Of those, he left some in uncut sheets of 9 which you see from time to time. Fun fact - when Bob printed them up, maybe intending to produce 500-600 sets, he realized the card stock was too thin for cards, so he glued 2 sheets together to make them thicker (taking us down to 250-300 sets). You will sometimes see cards for sale "with glue on the back" or "with glue on the front" - these are of course half cards, as over the years, the glue has dried out and some have separated. A set of 1967s just went a week or two ago on the 'Bay where a good run of the first several cards were half cards. Was still a nice looking set!
Happy collecting!