Yes my friend, indeed the men who spoke in the scriptures had the witness of the Spirit. As those who are saved have the same witness, and thereby can validate the witness in those who spoke.
This is very central, because without the witness of the Spirit ourselves we could not bear witness of the Truth.
I want to tell you about this witness. When I read some words of many of the Patriarchs the Spirit shows me their error. When I read Paul wrote something, I got checked and I knew Paul was speaking in the flesh, and not in the Spirit at a certain time, and it was confirmed when I read the next sentence in which he said he was speaking as a man.
Also, when I read about David, I knew when he was not in the Spirit, and in the flesh, because I was checked in my spirit by the Spirit of God in one of his cases. It is this same witness that witnessed through the prophets and that witnesses through the scriptures, but many people cannot hear this witness.
So when I say that Life is not in the bible, it is in Jesus Christ, we should be able to hear this witness.
May Jesus bless you.