[JLange]

Searched on GenealogyBank in PA and NJ for ads from 1952-56 and didn't get any hits at all using the search "mascot dog food." I expanded my search for the whole country, and got this tantalizing piece of info (photo) which came from the April 27, 1954 Evening Star out of Washington, D.C. in "The Baseball Beat" column by Burton Hawkins.

The text reads,
"Bucky Harris is a business associate of Al Rosen, Ed Mathews, Robin Roberts, Yogi Berra, Ed Lopat, Monte Irvin and Specs Toporcer. Their pictures appear on cans of Mascot dog food and they get a slice of the sales."

That's it! Sure would be great if those guys were on the remaining cards in the set!