Great question. There was already a validation method used by the scribes. See my brief chapter on Bible Transmission:
I read with interest Fred, of course another point that is forgotten perhaps the most important regarding transmission of the old testament is that it's conservation was a matter of religion and not just scholarship among the Jews, any addition to or taking away from the message [and this applys just as much to oral transmission although I don't accept there was of neccessity a time when the revelation of God was soley a matter of oral transmission] but any alteration was regarded as profanity.
I do not believe either that there was a period in church history when the gospels were passed on only by word of mouth. Jesus was always surrounded by scribes and they were not all opposed to him.
St. Luke states very clearly how his gospel was written, he says in verse one "Inasmuch as many have undertaken to compile a narrative of the things that have been accomplished among us just [exactly] as they were delivered to us by those who from the beginning were eyewitnesses and ministers of the word."
Mark we are sure is St Peters account, Luke and Matthew show ample sign that they drew upon a common source all the early doubts and criticisms of the 19th century scholars have been swept aside regarding their authorship and date of writing. Only John's gospel is still disputed [not among believers] among the scholars as to date and authorship and their only question is how could John, a fisherman, have had access or been privy to what went on among the sandhedrin and among the chief priests, on the basis of this alone they cast doubt upon the authorship of John the apostle.
But they forget all about Nicodemus who was very high up in the priestly caste and a teacher and secretly a follower of Christ, who was stood by the cross when he obtained permission to take down the Lord's body but John the apostle, can't tell me they didn't become life-long friends bonded together by grief.
Of course the Great Witness to the authenticity of God's word as it has been transmitted down the centuries is God Himself. whether Augustine in the 4th century or Wycliffe in the 12th Luther in the 16th, Bunyan, the Wesleys down to little ol' me we have proved it true by doing what it tells us to do i.e repent we have proved, countless millions have proved, regardless of s@x, culture, nationality or scholarship we have all recieved the washing away of sins and the new life full of joy and full of glory. We all say with a united voice this word is true and we are witnesses. I'll pop by again your page, I like that stuff