I am thinking it is essential for an elect to know about Christ Jesus one way or the other, by hearing/preaching or reading the gospel about Him... even in the early years. Belief by knowledge of Christ is absolutely necessary, that is what the gospel was preserved for... it is the disciples accounts of the life, death and resurrection of the Savior and they were eye witnesses and their message reveal for us the message of the truth. Jesus stated that those that came after the disciples would be blessed for believing in Him, but to believe in Him you have to have heard the gospel.
John 20:29 Jesus said to him, “Thomas, because you have seen Me, you have believed. Blessed are those who have not seen and yet have believed.”
So we have been given the written Word, the Scripture, for the express purpose to teach us about Christ, so we can believe in Him, through faith that comes from God.
John 20:30 And truly Jesus did many other signs in the presence of His disciples, which are not written in this book;
v. 31 but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name.
Only by the Spirit of Christ in us can we understand the gospel of Christ and that makes us part of the body, and we are united in the same beliefs and faith with other believers.
Eph 4:10 He who descended is also the One who ascended far above all the heavens, that He might fill all things.)
v. 11 And He Himself gave some to be apostles, some prophets, some evangelists, and some pastors and teachers,
v. 12 for the equipping of the saints for the work of ministry, for the edifying of the body of Christ,
v. 3 till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ;
v. 14 that we should no longer be children, tossed to and fro and carried about with every wind of doctrine, by the trickery of men, in the cunning craftiness of deceitful plotting,
v. 15 but, speaking the truth in love, may grow up in all things into Him who is the head—Christ—
I guess my point is that I cannot see how somebody can be an elect without the fundamental knowledge of the gospel of Christ in the Scripture. God could certainly bring about special circumstances so that any of the very few He has chosen to be an elect could learn the truth... if a person was illiterate (in the first centuries, since most people could not read), God would provide a teacher... so maybe that is the way they were taught in those first centuries, by being taught through preaching (Romans 10:14). But whatsoever would have been needed to teach an elect (preaching or access to the Scripture) I believe could and would have been provided.
mercy, peace and love
Kat