Not only is the papacy the longest continuously operating organization in western civilization, but, in true western fashion, there is a bureaucracy attached to it. Like all bureaucracies the papacy is fond of paperwork and lists, and since the third century has kept a list of every pope. Beginning in the renaissance it has been known as the Liber Pontificalis, the book of popes.
The quality of the entries has varied widely, everything from merely a name and regnal dates, to brief lives that include some background information and deeds performed while pope. Most of the lives were written during the lifetime of the pope, or immediately after their death. We are fortunate to have that sort of detail available for the eighth century, although the details vary considerably.