History indeed tends to forget Klaus.
The heavens wouldn't want someone like him to be remembered as a martyr; they will do everything in their power to erase his achievements, and so they have been doing the same thing for billions of years.
So, it's no wonder the Shadowless Assassin was the well-known assassin who shocked the universe.
Even she would have been wiped out if not for her positive karma, despite becoming the wife of the most hated existence.
Klaus was okay with that simply because he didn't really care about those histories anyway. It wasn't as if his memories were lost, and he had to rely on history to know his legends.
He could recall them easily, and now that he had more memories from his 9th incarnation, for now, he was okay not knowing other things about himself.
