HOW COULD DR'S NOT KNOW ABOUT SOMEBODY GETTING MEDS FROM DIFF DR'S PLZ HELP ME/HIS MOM VERY WORRIED FOR FRIEND?

ok so one of my good friends back home i guess was arrested for robbery and larceny all kinds of stuff to support his addiction to pain killers and his mom called me to tell me about everything that happened and asking if he called if i could talk to him and she told me that his fiancee was going around to like 8 different doctors getting prescriptions for oxycontin from each of them and me and his mom where both wondering how n the heck did none of these doctors not know about each other? or is it that the only way the doctors find out is if they call or email the pharmacy asking them if the person is getting multiple prescriptions? so if his fiancee was a good actor and liar and never gave them reason to suspect anything then the doctors would never find out. is that how it works where the doctor has to request the info in order to find out and its not sent out automatically or is it vise versa please let me know cuz we are really hoping to find a way to help him out of this addiction and ways to keep him from getting them again