In Greece there are different male/female variants of the same surname, so it would be normal for a married couple to have slightly different surnames.
e.g Papadopoulou vs Papadopoulos.
Then there are the cases where a Greek wife takes the male surname form to co-exist more easily in other countries where it is expected for a husband/wife surname to match (or if different, be more considerably different).
Because of that, my grand father and his sister happened to have different family name in their ID cards: when they got registered by the priest at the beginning of 1900, on a paper book of course, the priest who registered the sister added an "I" at the end of the family name as he thought that that should be the right spelling in proper Italian. At that time ID cards did not even exist so nobody bothered.