“I’ve found that he’s not licensed to practice medicine in that state.”
I have known Dr’s to miss this registration. It is huge fines and they can lose their right to practice.
A DR in the Philadelphia area was having an affair with the wife of one of my friends. He hired a PI who found out that the DR was not licensed to practice medicine in PA. It ended up being a real big and expensive oops.. fines for this are very high.
Here is a David V. Diamond
http://profiles.ehs.state.ma.us/Profiles/Pages/PhysicianProfile.aspx?PhysicianID=9206&Print=True
Why? The registering groups have laws to make sure they get their money?