I don't have the definitive answer but I do have a lot of experience with deep weight, finger and thumb holes. Since I try to get my equipment down to 14.9 to 14.11 (tops) due to a wrist/hand injury years ago my driller and I have devised various methods of weight reduction including the use of 12 inch drill bits to drill an X-hole almost through the entire width of the ball (yes, it's legal as long as the statics are within parameters).
Now, my primary driller does a great job of getting the weight down on balls that weigh in at 15.2 or less. However, as in the case of my No Mercy, it weighed in at 15.5. he got it down to 14.13 but it was just too hard on my hand. So, yesterday I took it over to the other driller that has the 12 inch drill bits. Since driller #1 had drilled the thumb very deep this driller will have to plug the thumb about half way up so that the x-hole doesn't run through the side of the thumb hole. He believes that IT IS ILLEGAL FOR TWO HOLES TO MEET.
It would be very interesting to get a definitive answer on this. All I know is that the driller with the 12" bits is a card carrying PBA member and was briefly on tour back in the 80's. So, I figured he ought to know what he's talking about.
