Advocates for sola scriptura argue that Christians need a written record since oral tradition is so given to inaccuracies and therefore untrustworthy. Aside from the fact that anthropological studies have demonstrated the extremely accurate fidelity of oral traditions in cultures for whom such traditions are central to their culture (unlike literate cultures such as ours), there is a very accessible way to demonstrate both the accuracy and trustworthiness of the oral apostolic tradition.
If one were to compare contemporary Christian writers, who were separated by significant geographical distance, and were writing before the full canonization of the Christian Scriptures, and even during the period when there was some dispute over which books were Scripture, and also during the period when many heresies had arisen, and if those writers provided a summary of the Christian faith, then one can readily compare whether or not the oral apostolic tradition is accurate and trustworthy. As St. Irenaeus of Lyon writes:
As I have already observed, the Church, having received this preaching and this faith, although scattered throughout the whole world, yet, as if occupying but one house, carefully preserves it. She also believes these points (of doctrine) just as if she had but one soul, and one and the same heart, and she proclaims them, and teaches them, and hands them down, with perfect harmony, as if she possessed only one mouth. For, although the languages of the world are dissimilar, yet the import of the tradition is one and the same. For the Churches which have been planted in Germany do not believe or hand down anything different, nor do those in Spain, nor those in Gaul, nor those in the East, nor those in Egypt, nor those in Libya, nor those which have been established in the central regions of the world. But as the sun, that creature of God, is one and the same throughout the whole world, so also the preaching of the truth shineth everywhere, and enlightens all men that are willing to come to a knowledge of the truth. Nor will any one of the rulers in the Churches, however highly gifted he may be in point of eloquence, teach doctrines different from these (for no one is greater than the Master); nor, on the other hand, will he who is deficient in power of expression inflict injury on the tradition. For the faith being ever one and the same, neither does one who is able at great length to discourse regarding it, make any addition to it, nor does one, who can say but little diminish it.(St. Irenaeus of Lyons, Against Heresies, Bk I, Ch. X, Par. 2)
Now, the historical period that would be ideal, in my view, would be the end of the second century, or beginning of the third. My reasons that this period would be ideal are these:
1. Although all of the New Testament books had been written, historical evidence indicates that not only did not all Christian communities have all of the New Testament books, but that some considered certain books divinely authoritative that others did not, some of which in fact did make it into the New Testament canon (e. g., Revelation) and some of which in fact did not (e. g., Shepherd of Hermas). Thus, given these canonical discrepancies, it would be theoretically possible for there to be equally discrepant practices and beliefs among these far-flung contemporary Christian groups.
2. Furthermore, given 1, there would need to be a great reliance on oral apostolic tradition, all the more so, if, as scholars generally assume, the vast majority of Christians at the end of the second century (and generall