Edelbrock AirGap question

I'm not arguing, because the good lord knows I ain't seen it all, but I've never seen that in print from a competent source in any publication. Ever. All I've ever read and heard was that the notch was there for the Holley 3916 and 4604.
It was in the DC engine manual, for one. I believe it was in Shepard's book, too- can't verify, loaned it out and hasn't found it's way back yet...