I just found something very interesting regarding area-ruling. I was reading this book called "U.S. Naval Air Superiority: Development of Shipborne Jet Fighters 1943-1962" by Tommy H. Thomason
There is a section on page 211 (Figure 13-1) which discusses the fact that Grumman actually seems to have figured out the benefit of Area-Ruling before Richard Whitcomb did. Did they derive this data on their own, or using Wallace D. Hayes' data?