Partly. Also from the testimony of others. But about the Bible in that regard: If I give you a book that I claim is a repair manual for a 1957 Chevy and am able to use it's instructions to successfully remove, repair and re-install the radio, what do you think my response is going to be to a person who says the book is baloney?
Of course, that person is entitled to his belief, just as the people in Iceland are entitled to their belief that my wife does not exist.
But so am I.
Repair manuals are written and REVISED as needed to correct mistakes. Are you saying that the Bible is revised to correct mistakes?