Comment by Petar Zrinjski:
Gregorian and Old Roman chant largely share the same liturgy, but Old Roman chant does not reflect some of the Carolingian changes made to the Roman liturgy. Both an Old Roman and a Gregorian version exist for most chants of the liturgy, using the same text in all but forty chants, with corresponding chants often using related melodies. The split between Gregorian and Old Roman appears to have taken place after 800, since the feast of All Saints, a relatively late addition to the liturgical calendar, has markedly different chants in the two traditions. The Old Roman tradition appears to have preserved the texts more faithfully; the Old Roman texts often resemble the earliest Carolingian sources more closely than the later Gregorian sources do.