I do not engage in scholarly editing, but I have great admiration for those who do, and I am very grateful for their efforts. I read the prefaces to the volumes of the Teubner and Oxford editions of classical Latin texts -- I've read a few prefaces to the editions of the Greek classics, too, although I can barely read any Greek at all -- and I'm thrilled by the stories of how this or that Classical text survived until our day.
"Survived" is the right word. And "dark," I believe, is a very appropriate term to describe the Dark Ages in Western Europe. I'm using the term "Dark Ages," not as synonymous with "Middle Ages," but only to describe the first part of them: the time between the fall of the Western part of the Roman Empire in the fifth century AD, and the rise of Charlemagne, emphatically punctuated by his crowning in Rome as Emperor Pope Leo III on Christmas Day, AD 800. Yes, this talk of a renewed Roman Empire was a little silly and presumptuous on the part of Charlemagne and Leo; no, the Empire which began in 800 never compared to the ancient Western Empire, nor to its contemporary the Eastern Empire, usually referred to in the West as Byzantine; and yes, Charlemegne's empire fell to pieces when he died, not least because he maintained tradition of Germanic chieftains of dividing his land among his male heirs, instead of the Imperial tradition of choosing one chief heir to rule after him and finding other occupations for his other legitimate sons.
Despite all of that, however, it does make a lot of sense to state that the Dark Ages came to an end with the reign of Charlemagne, and one very dramatic measure of this is the number of manuscripts of ancient, Classical Latin authors which survive today dating from the time of Charlemagne and later, compared with those dating from the time before. Aside from copies of the Bible and of Christian authors, almost all of those manuscripts date from the 9th century and later; then there are a few from the late Western Empire; and from the Dark Ages, almost nothing. Charlemagne gave massive support to monasteries, not just for doing things like copying Bibles and chanting hymns, but also for things like copying Classical texts. Although the Empire fell apart when Charlemagne died, the program of preserving the work of Classical authors survived and grew and flourished.
One of the many problems facing a scholarly editor of an ancient Latin text, attempting to produce the best version he or she can of that text, is that the very idea of preserving old manuscripts, of valuing them precisely because they are old, seems to have occurred to very few people before the past several centuries. And so the manuscripts which survive are mostly relatively recent, copies of copies of copies of... repeat a few times, or a lot of times. And just like in the game where people sit in a circle, and one person whispers into the ear of the person seated next to them, and that person repeats what they think they've heard, and by the time the whispering has gone all the way around the circle the result is comically different than what was whispered first, so a lot gets lost and changed as manuscripts are copied and recopied many times over the centuries, and the older copies get lost. Except that with the manuscripts, the original statements have almost always disappeared, and not many people think that the changes are very funny. On the contrary. This is one area where change is almost always considered bad.
So, any discovery of an old manuscript, from before the age of printing, is a great sensation in the scholarly world, and an especially old manuscript is a bigger sensation, because, it is hoped, it may be closer to the original text of the ancient author, and so it is diligently compared to the other manuscripts, and revisions of printed texts may be in order. Older is not always considered to be better -- not always, but most of the time, all other considerations being equal.
Before the idea of older manuscripts being better just for the sake of being older became widespread, however, the writing was sometimes scraped off of older parchments in order to make room for something else to be written. In such cases, the indentation left by the pen when the older text was written may remain although the ink of the older text is gone. These indentations are called palimpsests, and in the 19th century, in a new field of scholarship largely pioneered through the efforts of a Catholic Cardinal named Angelo Mai, many very old palimpsests began to be deciphered, and some texts which up until then had disappeared from the view of the scholarly world re-appeared: the letters of Frontofor example, Cicero's Republic, a large fragment of book 91 of Livy's History of Rome-- these and quite a few other ancient texts are available for our perusal today only because some whip-smart scholar somewhere, examining a manuscript, noticed that something had been written on it once and then scraped off, and was able to recover the text just from the indentations, from the palimpsest. In the late 19th century archaeologists began to dig up scraps of papyrus in Egypt with writing on them, mostly Greek writing but also some Latin and Coptic and other languages, scraps which had been mostly thrown away, but the ancient world's garbage is now our gold, because these papyrii were written on between the 2nd century BC and the 6th century AD, and remember the whispering circle, older is better, even an old raggedy scrap of garbage can cause a sensation if it contains a copy of a passage by Homer or Hesiod or Vergil centuries older than the oldest previously-known copy of that passage. Thousands of such scraps have been found, better methods keep on being found of deciphering texts on pieces of papyrus which in some cases have thousands of years' worth of dirt on them -- I don't mean to sound overly dramatic, but big things have been happening lately in the interesection of Classical scholarship, archaeology and other things like laser-imaging technology.
It's sort of a shame that the general level of interest in Greek and Latin antiquity has been dropping over the past couple of centuries, while at the same time so much more of that ancient world has been re-discovered.