TOTAL idle speculation; but Gehrig was sometimes referred to as "Buster" by teammates.
If it could be proven that it was related to your "B" on the knob, that would be very interesting.
You would have to get IRONCLAD proof (probably a very clear, unambiguous photo). I have never heard of Gehrig adding letters to the knob of a bat.
Better yet, find a photo of him holding it, and your bat goes from a few thousand to a few
hundred thousand.