Ben, SGC definitely misidentified the card; it is, for sure, a 1962 JELL-O. Then again, if the individual who submitted the card to SGC put on the paperwork "1962 Post Cereal", their people may not have noticed the error, and simply copied as correct.
I wish I could help with information on the smaller '62 Mantle. It is most unfortunate that it was cut off the advertising / store display. For one, the display would have been worth so much more in the potential information it might have disclosed, as well as money.
Being that the issue was indeed a test issue available only in the Chicago - Milwaukee area, any advertising pieces would be very rare. The 1981 Beckett Guide listed them as a regional. When I interviewed Larry Fritsch for my book, NEVER CHEAPER BY THE DOZEN, he confirmed the test issue nature of the '62 JELL-Os and that the area was Chicago - Milwaukee. Larry had a lot of first-hand experience with these, since he lived in Wisconsin, and worked on the railroad that ran each day from Milwaukee to Chicago. He stopped in stores in both areas!
Earlier this year, Bob Lemke uncovered a press release from General Foods that was placed in an early May 1962 issue of THE SPORTING NEWS. Within that release, it specifically mentions the test-marketing in the Chicago area of individual JELL-O boxes with a baseball card on the back of the box.
It's hard to say whether JELL-O produced in-store advertising for 1962. The advertising store display piece shown was probably from the nation-wide JELL-O baseball card issue in 1963. Even though it was nation-wide, it is extremely rare today. Nearly all of those placards would have been tossed in the dumpster after the promotion ended back then.
Now, Dan Mabay, who I believe goes by the moniker, "Keepmeposted", is researching the 1962 JELL-O set for a book. Maybe he would know. Anyone know the gentleman, or how to reach out to him? I for one sure want a copy of his research book when it is completed. I don't care how much it costs.
Thanks for sharing this find---most interesting.
Hope you get an answer. Please share with us.
Question---does the rest of the ad piece that the Mantle was cut from still exist, in order to learn from it? Just wondering.
Best regards, Brian Powell