Complex sentence: The only difference is that every chant is not represented by an incipit, it is fully notated in neumes and in alphabetic notation as well, so that even cantors who do not know the chant can memorize it with this tonary together with its tonus.
Split into simpler sentences: The only difference is, that every chant is not represented by an incipit, it is fully notated in neumes and in alphabetic notation as well. Thanks to this manuscript, even cantors who do not know the chant, can memorize the melody together with its tonus.