From what I just read in the book "Can't You Hear Me Calling" Mr. Derrington's job was made more difficult because there were TWO F-5's damaged and the pieces were mixed up when gathered. Mr. Derrington used a magnifying glass to help differentiate between the two instruments. The F-5 Mr. Monroe usually played had a slightly different cast to the finish and by careful scrutiny Mr. Derrington was able to effect the repairs (he fixed both instruments as I understand).

I prefer to cut James some slack. Growing up Bill Monroe's son was probably not the easiest life. Mr. Monroe's constant womanizing surely had a bad effect on his son. If James seems mercenary it is a family trait, sometimes leavened with unexpected generosity, and he sems to be his father's son.