Original sentence: While still largely accurate when it states something (only rarely has the ancient text cited changed), much is missing, especially more recent discoveries (like Aristotle's Constitution of the Athenians'') and epigraphic material; perhaps more seriously, the context in which ancient evidence is viewed has often changed in the intervening century and a half
Edited sentence: While still largely accurate when it states something (only rarely has the ancient text cited changed), much is missing, especially more recent discoveries (some of the greatest importance, such as Aristotle's Constitution of the Athenians'') and epigraphic material; perhaps more seriously, the context in which ancient evidence is viewed has often changed in the intervening century and a half