In addition to what has been discussed, remember that people's hands change over the years. Usually flexibility decreases with age, arthritis sets in, pitches are adjusted, sometimes we add pinky holes... There are always things to consider, so having an open mind helps.
Every bowler can and should get their specs tweaked periodically. One of our long time clients happened to see Bill Hall in Baton Rouge, who had made a few recommendations based on his expertise. We looked back and discovered that the specs for this guy were from several years ago. This bowler's physical shape had changed (for the worse) and so his game had very gradually changed. He never mentioned any troubles, so we assumed his grip was okay.
When he returned from Baton Rouge my friend (who has drilled maybe 20,000 balls over the past 25 years) remeasured his hand and was amazed at how much the two spec sheets differed!
The only reason I mention this is so those who read it will not assume that the "perfect fit" from 5 years ago may, or may not, be perfect today. Fitting hands is the "art", and drilling (hitting lines) is the easy part. Those of us who help others in this respect need to keep an open mind because there are no two hands exactly alike.
Thanks for everyone's input.