The researcher, translator and/or reader of any piece of Church literature must be cognizant of the fact that most ancient Church writings available today have a twofold interpretation process; the written and oral traditions.
The written is easier to identify than the oral. Since the oral tradition has been lost for centuries, it is the role of the researcher/translator to reconstruct this.
The importance of this is not so apparent, but as one translates and begins to find older texts within other works without citations, one will find the medieval community depended on the oral tradition for these points.
The Christian chronological tables are one of the best examples. Africanus was the first Church father to try and reconcile dates and history into a uniform time frame. Only fragments of his work called the Chronography, exist today. Eusebius published his own version based on this. We only have fragments of this work today. Jerome admittedly took from Eusebius’ timetables and created a more expanded version which we have available today called the Chronological Tables. The Chronological Tables set the basis for the 7th century Chronicon Paschal, which expanded the explanations even more. The Chronicon Paschale does not succintly mention Africanus, Eusebius, or Jerome in its citations.
It is a known fact that many medieval monks, copyists, and authors frequently inputted text from the ancient sages within their works and did not feel the necessity nor the importance of noting the original authors they quoted from.
There are always exceptions. The 8th century writer/scholar/teacher in almost any field, the Venerable Bede, was one of the few that did try to cite all his sources during this period.
Another problem example is Origen’s Catena on I Corinthians. It is by no means an old document, likely this version dates around the 10th century or later. It is intermingled with Eastern Attica and later Byzantine Greek. The Biblical citations use the Old Slavonic typeface. The grammar and vocabulary is very similar to Chrysostom. Some word usage can only be found in Chrysostom. One is not entirely sure if the text is totally true to Origen, or has some insertions from Chrysostom or an editor put in some later thoughts.
Some manuscripts depart from the original and demonstrate new thoughts. Some manuscripts such as Against Heresies by Epiphanius contained in Migne Patrologia Graeca is not really that old. Many parts are later additions. The copy that MPG used may even be a Greek translation of the Latin. However, there is an old remnant of Against Heresies found in St. Anastasii Sinaitae Questiones which one can compare and get a good idea of what the original was.
Still the newer copy demonstrates what the writers thought and interpreted their religious world to be in their epoch. It has important value for tracing a religious doctrine or movement throughout the centuries.
One must understand this is not a bad thing, nor a conspiracy by the Church to hide, correct or improve problematic texts. The medieval period was a transition time between oral and written communication. Most of the population was not literate and there was still a heavy dependancy on transmitting Church doctrine, law, practice and interpretation orally. The oral tradition worked almost evenly alongside the written text. The making of handwritten texts were a long, expensive and tedious process and was not a process that would allow for the general population to have copies in their own home.
The oral tradition was very important because illiteracy was also very high. Harry Gamble outlines literacy and the role of oral and written tradition in, “Books and readers in the early church: a history of early Christian texts.” This is written more about the early Church than the medieval age, but it appears from a literacy perspective to still hold for this period as well.
This oral tradition over the years became disrupted, and much of the wealth that was contained in such knowledge was lost. The medieval monastic orders orally knew which parts of the chronologies to ascribe to Africanus, Eusebius and Jerome but this was never written down. Today, since this tradition was lost, we do not know exactly in many texts who said what.
What does this all mean then? When one cites Origen, Ambrosiaster, Jerome, Epiphanius, or any other ancient writer, be cautious, just because they are listed at the header of the document as the author, they may not necessarily be so. It may be a later tradition based on that author or an uncited text from another author.