OK, you are deep into this then! Makes it even more fascinating. Actually I have been talking trepanning a lot lately with my youngest daughter. She has suddenly developed a great interest in history, so every evening while my wife was travelling the world we went through the prehistoric ages that she is learning about in school and we went to the National Museum to see some of the things we had been talking about. Here we saw this:

It is a 5000 year old skull with a trepanning that worked. The man was about 30-40 years old when he died and he had lived a long time after the operation as you can see by its smooth edge. I remember the skull from my own childhood, but my daughter was so fascinated by it that she had to go with her mother too when she came back.