This topic is old, but wanted to add this from an interview with Marko Prezelj, another Slovenian alpinist and one of the greatest Himalayan climbers of all time:
We mentioned Tomo Cesen. So the simple question is: did he do it or didn’t he?
He did it. There’s no proof that he did it and there’s no proof that he didn’t. So to me, as long as he says he did it, I believe him. Almost every alpinist in the world has something they did without proof. So if I started disbelieving him, I’d have to start disbelieving others. I have many ascents I have no proof I have made. Even in sport climbing you often have to just believe that someone’s done something. Without any proof. So for me this kind of trust is a fundamental thing in climbing. Besides I know Tomo, and it helps me to believe, because he’s a really special person who is able to do such things.