I’ve always believed that there’s only one truth. Whether we are aware of that truth or not, it remains true, nonetheless. (A blind person who doesn’t see a book on a table doesn’t make the book any less present).
That which was written in the New Testament, then, was true even before it was written, even though people weren’t yet aware of this truth
Were people who lived in, say, 100 BC subject to the teachings of the New Testament?
Is there a possibility that another Testament could be written in the future? If so, we might not yet be aware of future teaching that is already true.