I have heard that before his untimely death Mr Kelley was planning to do more work on the computer section of The Golfing Machine with Dr Mumford.
Make of that what you will.
Homer Kelley never met or considered working with Carey Mumford. Long after Homer's death, Sally Kelley was approached and asked to consider expanding Chapter 14 with Carey's material, but the plan never materialized.
Homer knew that his book identified only the "bare-boned identities" of the subject matter. In fact, his intention to deliver a "one volume Handbook" dictated its extreme brevity. That being the case, he also knew that, "because of questions of all kinds, reams of additional details must be made available -- but separately and probably endlessly" (1-H). [Bold emphasis mine.]
I, for one, am glad Sally decided to respect Homer's wishes.