I am wondering why I hear these differences in chant recordings I have heard:
1) Sometimes I have heard the Introit sung without the Gloria Patri, or with it before the Introit verse is sung a third time.
2) Other times, I have listened to the Alleluia just sung with one Alleluia at the beginning instead of two.
3) I have heard the Communio alternating with Psalm verses before. And I think maybe the Gradual at least once too.
What accounts for these various ways of singing chants at Mass?
I thought they were supposed to be sung normally like each way respectively:
1) The Introit with Psalm, Gloria Patri, and repetition.
2) The Alleluia sung twice with verse and sung again once.
3) The Gradual and Communio each sung once.