I'm not a historian (I don't even play one on TV), so it's genuinely possible that I'm missing something here. However, am I to understand that when writing a biography, as long as you have sources making a claim, you can include this claim in your book as fact no matter how true it might be? Does this mean that if I say I'm the King of Finland, then years later someone writing about me can say "Veleda was the King of Finland," no matter the evidence that this was not in fact the case?

......I'M THE KING OF FINLAND. WOMEN HAVE FOUGHT AND DIED FOR THE LOVE OF ME. YOU HEARD IT HERE FIRST F_W.