We're pretty sure Ninevah didn't convert to Judaism en masse, as in Jonah. In Job, it reads very much like a fictional story based on a real man, or even complete fiction. Other wisdom books claim authorship by Solomon, but most scholars don't think Solomon wrote them. He was a figure who represented wisdom, and was perhaps used to give authority to the books under his name. I am agnostic on whether or not Tobit and other books are fiction, since I haven't heard any arguments either for or against that position.