Just that really.
Years ago, you were a doctor if:
a) you had medical degree
b) you had a Ph.D. Though strangely, many women were still called "Mrs".
Suddenly, dentists began to call themselves "doctor". As did vets. Then the practice (prescribing) nurse had "Dr. Joy Full" on her door, and now I see the physio is Dr. Payne-Legge.
I seem to remember that in Italy, lawyers are "dottore/dottoressa" (might be wrong), and anyone with a degree in Japan is entitled to be addressed as "sensei".
Yes yes, I know that "doctor" simply means "someone with learning" from the Latin.
Meanwhile, surgeons remain "Mr./Ms. McCUTcheon".
Will those attaining a 3rd in Media Studies soon be eligible to join the elite?