I saw this claim today on a puzzle site (crosswords, quizzes, etc.) I frequent, so I did a little research and found this article. I guess it’s possible that Norman Gibat had never seen such a puzzle when he created his grid of hidden Oklahoma cities, but I was born in 1959 and had several activity books as a kid. I’m almost certain that some of these volumes that were purchased before I turned nine featured “word seeks”, “WonderWords”, or whatever the creators called them.
Does anyone else remember pre-1968 instances of this diversion? It would be great if some Doper had actually kept an example and could scan it onto a personal page for our viewing, but I’ll settle for anecdotes that confirm my suspicions.