There was no difference in German, it was "Herr Doktor" ("Mr Doctor") and you'd address his wife "Frau Doktor" ("Mrs Doctor"), so you couldn't tell who of them

There was no difference in German, it was "Herr Doktor" ("Mr Doctor") and you'd address his wife "Frau Doktor" ("Mrs Doctor"), so you couldn't tell who of them actually held the title (not sure what happened after divorce). Today, you need to get your own title, no more shared titles through marriage.