One thing that did not exist 3,500 years ago was the History Channel. But this has long existed in Heaven and any angel of God can pull up any episode they want to observe. When the OT was first written down by the Yahwehist, this prophet had access to the History Channel and could write accurately from any timeframe, without relying in hearsay from previous generations. When it was written, it was accurate in the language of the time. When it was rewritten after returning from Babylon, it was no longer purely the Word.