Also, the Bible is unusual since it treats itself as so authoritative that rather than needing other sources, it is itself sufficient as 'THE' source. At the same time though, it was more accountable in its transmission than is known, since those who falsely prophesied were put to death even from long ago.
Deuteronomy 18:20 But the prophet, which shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die.
21 And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?
22 When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.
Zechariah 13:3 And it shall come to pass, that when any shall yet prophesy, then his father and his mother that begat him shall say unto him, Thou shalt not live; for thou speakest lies in the name of the LORD: and his father and his mother that begat him shall thrust him through when he prophesieth.
This is a pretty strong standard of accountability for Biblical authors. If they said something would come to pass and it didn't, they were put to death. The Bible itself declared it necessary to kill those who claimed to be prophets without being accurate as an assurance for its truthfulness.
Furthermore, there are other sources than humanity. A book could for example use sound logical reason, statements about the universe, human nature, nature in general, etc. If right often enough about readily verifiable facts, it would begin to build up for itself a record as accurate and consistent - by which to support its more extravagant and less verifiable claims - so long as they weren't certifiably false through self-contradiction or undisputable witness to the contrary. Especially if these were cited well before their time when such facts weren't readily accepted, it would be evident as more accurate on even controversial elements.
And actually, there is a very strong witness from history and archeology that has shown the Bible accurate on numerous disputed points. In some cases, it appears almost coincidental that history preserves so strong a record of Biblical events merely to prove them right. The Bible also provides names, dates (such as those according to the Persian calendar in the famous Daniel 9 prophecy), locations, etc. for historical verification. It is not afraid to cite facts about nature or facts about the universe or anything else for independent verification.
Ultimately, if God is the author, it wouldn't make sense for him or to defer to humans or their writings as his sources, since he'd be above them - they should be sourcing him. But he could use the historical record and nature itself as a means for verifying the book to those who might question it.
Edited by Jzyehoshua, : No reason given.