Papyrus meant two things: documents and books. On both scores, these Greeks on the Egyptian fringe could fill blanks in the record.
The traditional classical world leaves us only the grand official documents it inscribed on stone. Oxyrhynchus yielded a huge random mass of everyday papers private letters and shopping lists, tax returns and goverment circulars...maybe 50,000 in all.
The traditional classical world leaves us no actual books: the great Library of Alexandria, the twenty-eight public libraries of imperial Rome have disappeared without trace. We are left with copies of copies, chance survivals through the Empire and Middle Ages. We have ideas of whats missing, but these losses seemed final.
Sporadically and in fragments, the dumps of Oxyrhynchus are changing all that. Oxyrhynchus restores to us authors famous in classical times, who went under in the Middle Ages: the songs of Sappho, the sitcom of Menander, the elegant and learned elegies of Callimachus that Roman poets liked to boast of imitating. These Egyptian Greeks read Greek tragedies that to us had just been names and the satyr plays that went with them.