“Let me rephrase my response. The compilation of scrolls that comprise one physical book (OT and NT), did not exist in 325 AD.”
I’m going to ignore the absurd comment about the Old Testament, but as to the New, how do YOU know that? What we do know is that Ignatius, Polycarp, Irenaeus, and Papais, within the 1st and 2nd century, knew what were the 4 Gospels, and quoted from virtually every book in the New Testament except for 2 Peter and maybe Jude. Origen in the 3rd century discusses EVERY book of the New Testament, long before 325AD. So what the heck are you even talking about? You think Polycarp didn’t have a compilation of scriptures that he was quoting from? Irenaeus too? You think Origen didn’t know what he was talking about until a hundred years after his death?
As far as having physical copies of documents, in that day, as in our own day, there's a tradition of oral transmission just to make sure the written record is an accurate copy.
Other religions do the same thing and have sects devoted specifically to memorizing the scriptures as they understand them.
The OT still contains the instructions for setting up a MEMORY PALACE so you can memorize both it and the scriptures comprehensively. Actually, there's several memory palaces right there in Genesis.