I became something resembling in some ways an historian because over and over, I've read books on historical subjects, and I'm full of questions on the historical subject at hand which the book at hand does not address, let alone answer.
A wonderful exception to this rule is Texts and Transmission: A Survey of the Latin Classics, edited by LD Reynolds, which consists of 134 entries by 14 authors including Reynolds, MD Reeve, RJ Tarrant and M Winterbottom, each entry succinctly describing what was known, in the early 1980's when the volume was prepared, about the manuscripts and editions of each of 134 Classical Latin authors and anonymous Classical Latin texts. "Classical" means pre-Christian poems, fiction, history, philosophy, rhetoric and technical and scientific writing. In the case of Latin, Classical means things written for the most part between the 3rd century BC, when the earliest Latin poems, plays and historical writings which have survived were written, and the fifth century AD, when Christians came to dominate not just the governments of Latin-speaking Western Europe, but its literature as well. Reynolds admits that not everyone will agree completely about which authors and texts belong to Classical Latin. However, few if any experts would add or subtract more than a half-dozen authors and texts to or from Reynold's list.
Texts and Transmission is chock-full of things I wanted to know. Particularly wonderful and informative is Reynolds' Introduction to the volume on pages xiii through xliii, an extremely succinct summing up of the entire subject of the transmission of Classical Latin texts. On pages xvii through xxxii, Reynolds writes a much better summary of the Carolingian Renaissance than I ever will.
The Carolingian Renaissance is the renewed study of the Latin Classics done with the support of Charlemagne and his heirs in the 9th and 10th centuries AD. In the midst of Reynolds' description of this renewal, on page xxviii, is a list of 68 Classical authors and anonymous texts, just over half of the total of 134 discussed in the entire book. For each of these 68 authors or texts, there are one or more 9th-century manuscripts known to scholars today.
The Dark Ages is the era from the fall of the Western Roman Empire in AD 476 until the rise of Charlemagne, who was crowned Emperor in Rome by the Pope in AD 800. It's called "dark" in part because the written records of that time are quite sparse. This scarcity of written records in turn makes it possible to speculate about just exactly how bad or good things were in the Dark Ages. And hey, what a coincidence: historians who are Christians tended, by and large, to portray the era as having been much more pleasant and productive and learned and so forth, than historians who are not Christians. Almost everyone on all sides is biased.
But if we're only talking about the survival of and interest in classical Latin literature, then there is no doubt that "dark" is a fitting adjective. There are dozens of surviving Classical Latin manuscripts made before the Dark Ages. From the 7th century, the middle of the Dark Ages, there is 1, a manuscript of Lucan. C Hosius, whose edition of the 2nd-century Roman author Aulus Gellius appeared in 1903, described one manuscript of Gellius as "s vii(?)," meaning he was guessing it was from the 7th century. In Texts and Transmission, PK Marshall describes the same manuscript as 4th-century, with no ?.
Of course, the numbers of manuscripts surviving today from a certain century are not the same as the total numbers of manuscripts made in that century. Manuscripts have been thrown away, used to make covers for other books, burned in furnaces for warmth, destroyed in wars. As recently as the Renaissance, writers described many manuscripts which are gone today. In the meantime, the efforts to preserve them have become more energetic. We don't know how many Classical Latin manuscripts were made altogether in the 7th century, or the 9th. But the fact that we can locate exactly 1 from 7th century (or just possibly 2, but probably 1), and manuscripts for 68 different authors and texts from the 9th, is a very strong indication that some things changed in the 9th century, and that a lot of things were rescued in the 9th century which were on the verge of disappearing altogether. It also fits with what contemporaries wrote about Charlemagne and his activities, how he built schools everywhere and whatnot, and also with what we know about powerful Dark Age figures such as Pope Gregory the Great, and their disdain for non-Christian literature.
(Today, we have hundreds of 7th-century Latin manuscripts from the Bible and other Christian texts, and dozens of 7th-century Latin texts having to do with law, medicine, grammar and surveying.)