#19 "Addams was my first thought. I can't find it in the half dozen or so collections I can locate, and I'm not about to try to find it on the New Yorker CD-ROM, either. (Mild irony that it was most likely a New Yorker cartoon to begin with.)"

It's in Black Maria. However, it appears that it was not published in the New Yorker originally, because the book lists the dates of the cartoons that were in the New Yorker, and it's not on the list.

Charles Addams did this cartoon in the New Yorker, probably in the early 1950s. I've seen it in anthologies. Since he was one of the most prominent cartoonists of his time, it's highly likely that all of the artists mentioned saw his version.

That said, it's possible that the copying was done unconsciously.

There's no copyright issue, because story ideas cannot be copyrighted.