I think that we agree on the basics. Any man who believes in Messiah, or Christ, whether looking forward like Moses, David and Elijah, whether on the spot like Peter, or whether looking backward like you and I, is born again. The proof of this is irrevocable. Moses and Elijah were on the Mount of Transfiguration in Matthew 17, and that was the Kingdom according to our Lord Himself. And David will be raised a king of Israel (Jer.30:9). Only one born again can see the Kingdom (Jn.3:3-5). What we stumble on (both of us), is that we work in time and God is not so restricted. I will explain my viewpoint thus.
God is eternal. He has no beginning and no end. But God is a Spirit (Jn.4:24). The God-Man Jesus had a beginning. Jehovah says, of Jesus, "this DAY I have begotten you". Both "day" and "begetting" had a beginning. What happened is that the eternal God ADDED something to Himself IN TIME - humanity. Now, this where we come to the limits of our intellect. Was our Lord Jesus born 4,000 years after Adam in Bethlehem, or was He the "Firstborn of Creation" (Col.1:15). Well .... BOTH. But this offends the human intellect. In TIME it is EITHER, OR! It cannot be both. But it is BOTH. God says so in His immutable councils.
The paradox lies in the limits of the human intellect, not in God's Omniscience. WE may ask, how is it that our Lord is before Abraham, or even that He made everything Himself the Man being the first of this creation. But His crucifixion was "from the foundation of the world". My answer is, anything that the eternal God adds to Himself in time is added to His deity and becomes everlasting - that is, not subject to time. So although our Lord is not the first man ever raised from the dead, He is nevertheless "the Firstborn from the dead". But for our limited intellect, God reveals a SEQUENCE to teach us the grand truths. And the grand truth is that God wanted men. He wanted men to display Him by being the only creature in His image and likeness. And He wanted man to be His House - His dwelling on earth. So to achieve this, God sets a sequence of events IN TIME that explain the process that has become everlasting.
This sequence is, (i) incarnation - the Second Person of the Godhead takes human form, (ii) human life - the God-Man lives through all the experiences of life, (iii) human life under Law - the God-Man establishes a righteousness in all the demands of God, (iv) human obedience OUTSIDE of Law - the God-man agrees to the will of the Father to die for the guilty - something NOT required by Law, (v) human death - His deity is untouched because it is eternal, but He dies like every other man, (vi) human resurrection - to experience Hades first and then be made alive again in a glorified body, and (vii) human vindication - He is approved of God by being seated in God's Throne, but must still be set on His Throne over the earth (that is why no Christian should seek political office. His Master has not yet done this and should have preeminence in ALL things.
In this process OVER TIME God shows the ADDITION of human attributes ADDED to the Godhead so that when God does infuse a man, the man receives the accomplished work of Christ as a PACKAGE. For instance, 1st Corinthians 15:45 says that the "last Adam BECAME the life-giving Spirit". The word "BECAME" implies that He was not that before, but now is. But this produces a difficulty. The Spirit with His power to resurrect was there in all eternity. YES, BUT .... God wanted to add this to MAN. It is:- "The last ADAM", indicating that the Last Adam, Jesus Christ, has the power of resurrection in His humanity. And so He is able to say in John 10:18 that He has the power to lay down His life and the power to take it up again.
Now, in John 7:39 our Lord Jesus had gone through nearly the whole process IN TIME. Incarnation, human life, a Man under Law, and a ma obedient to God outside of Law, were all accomplished. But a very important factor was missing. The wages of sin is death, so if our Lord Jesus had failed to atone for just one little itsy-bitsy sin, He could not be resurrected, and we would still be in our sins. So the resurrection of Jesus was not only to add resurrection to the God-Man, but it was God's irrevocable proof that all sins had been dealt with. Until this proof was established, the God-Man, as the Spirit which gives to men the full PACKAGE of the God-Man, could not be given. This is the process of establishing the full human experience into the Godhead, so that He can dispense Himself into man and have men LIKE HIM. It was established in TIME by a series of events. But when added to Deity, it became everlasting.
So you are right. Adam believed God concerning Eve's Seed. Adam did not have full knowledge of the atonement work of Christ, but he believed and called Eve "mother of the LIVING". Abraham and Job followed, believing in the RESURRECTION even though they were sinners. Moses and David had a better view of Jesus, but their view of Jesus was enough for FAITH to do its work. Peter is given a vision. Paul is given a vision. And every Christian looking back on, and who believes in Jesus, THOUGH HIS KNOWLEDGE IS NOT COMPLETE, is born again and receives the Spirit of John 7:39. How can we be sure? Because in 2nd Timothy 2:10, "... we obtain the salvation which is in Christ Jesus with eternal glory." And in Hebrews 5:9; "And being made perfect, he became the author of eternal salvation unto all them that obey him". The salvation of Jesus Christ has BOTH eternal glory and is eternal. But the AUTHOR of this salvation "BECAME ... !" That means that He was not the author, and then went through a process that made Him that later.
I define this a "LOGICAL MYSTERY" - a contradiction in itself, but nevertheless TRUE. It is so logically set forth in God's Word, but it possesses a factor that the human intellect cannot quite grasp. Which just shows how high our God is, and that we should bow our knee that He even deigns to reveal this to men.