I was given a Groove that is now on it's third finger drill and 4th thumb. All the thumbs are in nearly the same place though so it looks like a large shamrock with a hole in the middle. The ball is still excellent.
Edit: Regarding the core, if drilling into the core alters the reaction of the ball, does this mean that Visionary balls are more unlikely to be affected by mass redrillings as the opposing lighter flip cap allows drillings to not hit the core of the ball?