Before the NT was canon, the OT was well defined. It was to these OT books the Epistles referenced when they referred to Scripture. The Church produced copies of Scripture through hard working scribes before the advent of the printing press and that made the books rare and very valuable in any parish. For this reason, they were protected in the churches and made available for study but not for removal.
But if that were the case how could Jesus hold men accountable to it?
Exactly! Before the Canon of Scripture was defined, there was the Church. Men were held accountable to the Church and her teachings. It can be fairly well demonstrated that personal interpretation of the Scriptures outside of the Church's teachings has led to disunion in the Church, not unity as Christ prayed for us.
The Apostles brought traditions and oral instruction, not books of the Bible (there wasn't one yet). See 2 Thess 2:15, 2 Thess 3:6 and 1 Cor 11:2 for proof this assertion.
Not according to the New Catholic Encyclopedia:
St. Jerome distinguished between canonical books and ecclesiastical books. The latter he judged were circulated by the Church as good spiritual reading but were not recognized as authoritative Scripture. The situation remained unclear in the ensuing centuries...For example, John of Damascus, Gregory the Great, Walafrid, Nicolas of Lyra and Tostado continued to doubt the canonicity of the deuterocanonical books. According to Catholic doctrine, the proximate criterion of the biblical canon is the infallible decision of the Church. This decision was not given until rather late in the history of the Chruch at the Council of Trent. The Council of Trent definitively settled the matter of the Old Testament Canon. That this had not been done previously is apparent from the uncertainty that persisted up to the time of Trent (The New Catholic Encyclopedia, The Canon).
Cordially,