Is it true that "Mrs. Doctor X" means "a wife of Doctor X" and not that the lady herself is a doctor?
But nowadays "Frau Doktor" usually refers to a woman who is a doctor, as "Doktor" has a male grammatical gender, so it's awkward to address a woman only as "Doktor X", even though that's technically acceptable. The grammatically female word "Doktorin" has not caught on, even though it's also correct.
Fifty years ago, could be either.
Nowadays, no.