Nowadays the Drop 2 and Drop 3 7th chord voicings for guitar are well-known, especially in Jazz circles. I don't remember hearing about these when I was reading Metal Solo You Can't Play Monthly back in the 80's. I have Chuck Wayne's "Guitar Studies - Chords" book wherein he basically claims to have invented or at least independently developed this system decades ago (50's?) without ever calling it that (but he didn't publish until the 90's). I have also heard that the "Drop __" nomenclature comes from arranging but can't substantiate this.
So my question is what were the first books / schools / artists to introduce Drop 2 and Drop 3 (etc.) voicings by that name as a thing to be learned and where did the concept originate?