Comment by roryirvine

The same thing happens in English literature of Dostoevsky's period - upper class characters might be referred to by substantive title (sometimes in two different forms), subsidiary title, courtesy title, surname, first name, job/rank/office, epithet, nickname, or even pet name.

To add confusion, the choice of which to use is usually context-dependent (time period, age, status, situation, relationship between characters) but sometimes the author will switch between, say, title and surname within the same paragraph simply as a matter of style or to avoid repetition.