Early attestations of the FANBOY(S) acronym

My earliest and still most popular post on this blog was about the FANBOYS mnemonic for recalling the "coordinating conjunctions": for, and, nor, but, or, yet, so. At the time, I wondered about the source of this notion. While not pinning down the source, Karl Hagan has found a 1951 publication mentioning FANBOY (without the S).

"The earliest source (so far) is Learning to Write by Reed Smith, Bill Paxton, William Paxton, and Basil G. Meserve, 3rd ed. Heath, 1951. Google only gives a snippet view, but that's enough: '[the] chief co-ordinating conjunctions are sometimes called the fanboy words.' (p. 398)."

And then the full acronym:

"The next work found in Google Books, and the first that actually gives FANBOYS as an acronym, is dated 1970:

Gertrude B. Corcoran, Language arts in the elementary school: a modern linguistic approach, Ronald Press Co. 1970, p. 140:
'Coordinating conjunctions can be remembered by thinking of the acronym FANBOYS'."