I guess my real point was that thumb pitches are subject to trial, coming down to what works for you & your game. I was happy I only needed one change of pitches to get to what I'm comfortable with.
I was not so lucky. A decade, or a dozen years or so ago, the ball drillers all decided that instead of the stretched grip we had all been using for some time, people needed shorter spans. OK. But at that time they failed to realize that shorter spans require thumb pitch adjustments.
When I became tired of dropping the ball, (which took longer than it should have) I did some research, dragged a ball I trusted out of the closet, and went to my driller. That summer, we replaced the slug SIX times until I got to someplace I was comfortable with. Yes, I paid for each one...it was worth it to me as an experiment.
I forget/don't have the paper work to tell my old span and pitches, but right now my thumb is 7/16" forward. Some is due to lack of flexibility in my grip fingers requiring away pitch for them. They are plenty strong, just not so flexible.
Once I was comfortable, I had them make a mold of the thumb, pitch and all. ALL the balls I have drilled since have had a copy of that mold installed. Even my spare ball. They all feel identical, and I like it that way.
my method may not be for every bowler nor driller, but it seems to have worked for me. YMMV