My friend just told me about this post. Here is what I know.
I have a complete set of Champion Cornflakes FB cards all SGC-graded (minus the Namath). They are in the large Beckett Annual guide. 15+ years ago a football dealer in San Diego who use to specialize in odd football and advertised in the back of the SCD, had some for sale at very steep prices. He probably provided the data to Beckett as "Champion Cornflakes". I helped add to the checklist over the years as I made some futher acqusitions.
Both Mike Moiser and I bought a small group about 6 years ago at a Ft. Washington Show from a local weekend warrior dealer. He had no clue, he bought them as part of a collection of baseball cards. Prior to this purchase we had our doubts, but we both concluded they were the "real deal".
They are all cardboard stock. They all had a consistent "nib" on the borders as if they were connected at some time. There is no way these could have been cut from a poster. I was able to buy another group to upgrade and finish (almost) my set from a person in Philadelphia who told me he had two blank ones with no picture. I quicklyhoned in on these. I asked him to find me a box, but unfortiunately he never did. These may have been prototypes that were never issued. They probably never got per got permission to issue Little or Rentzel.
I don't think SI was in the business of printing poster with no player images on them as there would be a very limited market for these
Also, I have an SI ad from a magazine. The players on the checklist do not match 100% the players on the magazine checklist.
Very little is known about this issue, but If I collected baseball I wouldn't hesitate at all in bidding on these. I have never seen them before.