I am going to repeat myself:
"I have completed the entire game, all DLC, all quests. The entries for Geralt and Gaunter O'Dimm are there and intact. They are still there in NG+ . This is a corrupt installation that does this, not the game."

Warble of a Smitten Knight does not cause this, nor does any other quest. The fact that a few other people have this issue does not preclude it being a corrupt installation, or saved games corrupted by that or something else.

This is a significant 'bug'; cosmetic, but still significant, so if it were the game at fault there would be thousands upon thousands of people complaining about it. There are not.

I've found another topic about the subject on CDPR forum (i still can't post any links, sorry). Moderator suggested to do something with patch files, i'll try this at home.

Excuse me, Hickory, I don't quite get your meaning. If it's not the bug then what is it? I don't know what causes it - corrupt saves or quests, or patches, or something else. At first I thought that it was only me who has this problem but it seems there are some other guys with this bug (or whatever it may be).

My meaning is clear. Read it again.

Anyway, I have loaded my old save before Warble of a smitten knight quest was started and, well, started it. It appears that this quest is really the source of the problem (at least in my game version). Last time geralt's glossary entry was intact I was training to shoot and strike from horseback before signing up for the tournament.

And right after the dialog with the guy who signs you up (I have exhausted all the dialog options - about Geralt being named Ravix of fourhorn and such, and have chosen Geralt's own name instead of Ravix) Geralt's glossary entry was gone.

I have continued this quest to the point where you can choose to continue to participate in the tournament or to leave it - and O'Dimm's glossay entry was there. And after i finished the quest (I have beaten the opposing team of knights and Gregoire de Gorgon then helped Guillaume to lift the curse from Vivienne) this entry was gone too.

So, to sum things up, it is all about some sort of bug during Warble of the smitten knight quest. I can't tell if this occurs on every system in every Witcher 3 game but my version clearly has this flaw.