Players' last names have been changed
 

After loading a saved game I found out that approximately a half of the players' surnames have been changed to Smith. Including retired players, stuff and so on. What happened? And how to change their names back?

It sounds like the names.dat file has gotten corrupted. The first thing I would try is going into the save folder (the one ending in .lg in the saved_games folder) and copying the names.dat file from the rs_one folder (your first rolling save backup) into the main folder, overwriting the one that's there. If that doesn't fix it, try the one in rs_two. If that still doesn't work, starting a new game (of the same type as your save) and copying the names.dat from that one should do it. You may see a few oddities with the naming after that since it may not be a perfect match for the corrupted file, but nowhere near what you're getting now.

Thank you. Your advise really helped! The names changed to normal ones.