Okay, I pulled out my paper copy of Comic Book Artist #5 (Summer 1999), which has an interview with Sam J. Glanzman. This is from page 96:
CBA: What comic books did you draw before World War II? Ron Goulart's Great History of Comic Books credits you with an "Amazing Man" story for Centaur.
Sam: So who the hell is this fellow, Ron Goulart? Anyway, the guy is wrong, wrong, wrong! My older brother Louis Glanzman (a.k.a. "L.S.G." or "L.S. Decker" drew the "Amazing Man," not me!!!
Barring any extant evidence to the contrary, the Who's Who is wrong, wrong, wrong!!! Thanks for making me do this research. I had forgotten where I had read that.