Dear Brother Timothy? As the first generation believers had no “New Testament” (it had not yet been written) to consult, did they remain faithful to the “thus saith the LORD” passages of the Law and Prophets?
Consider that the Apostles had, or were writing the Gospels & letters of the New Testament. The Apostles knew that these letters needed to be shared among the churches, as referenced in this verse: Colossians 4:16 And when this epistle is read among you, cause that it be read also in the church of the Laodiceans; and that ye likewise read the epistle from Laodicea.
And to answer your question, yes the Old Testament was relied on until the New Testament had been completed. This example from 2 Timothy is a good indicator: 2 Timothy 3:14 But continue thou in the things which thou hast learned and hast been assured of, knowing of whom thou hast learned them; 3:15 And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus
Once the last of the letters were written, which is Revelation, we find that these letters had been diligently copied and shared with all the sister churches. The Blood bought Christians of that day starting with the 1st century throughout had the new testament… It was then by the providence of God that these were compiled into one testament, The New Testament.
The Lord Jesus made sure that his final book, Revelation was shared among all the churches when told John to write: Revelation 1:4 John to the seven churches which are in Asia: Grace be unto you, and peace, from him which is, and which was, and which is to come; and from the seven Spirits which are before his throne; This was to signify that all shared in this final book of prophecy as was the case with all the Apostolic letters.
So to summarize Madge, yes they did rely on the Old Testament but it wasn’t long before the New Testament was fulfilled.
In the 2nd century, the Waldeness church of the Waldensian valleys of Italy, were the first to translate the New Testament from Antioch, Syria into another language (common or vulgar Latin) from the common Greek it was written in. This was called the Old Italia Bible. This complete and very accurate translation survived in it’s entirety until and after Erasmus took the complete Greek New Testament and compiled it to be used to translate our King James Bible into English. The Old Italia was used to compare the translation of the King James afterwards, and there was little, if any differences.
The Word of God itself says: Psalms 12:6 The words of the Lord are pure words: as silver tried in a furnace of earth, purified seven times. 12:7 Thou shalt keep them, O Lord, thou shalt preserve them from this generation for ever
Trust God! He does, and will continue to preserve His Word forever.