As always, I note the kind contribution of Richard Chonak who translated the Latin original of the second edition (1988). What do you make of the pastoral adaptation permitted below?
For like reason permission is given to choose among pertinent chants of the Proper of the Seasons, as for the proper text of the day another text of the same season may be substituted, if appropriate.
This seems sound to me, and an out for the “new music of the week” syndrome so often (and appropriately) criticized in the early post-conciliar years. The “like reason” is to “generously satisfy” the pastoral needs of any or all individual communities. By the standard of the Roman Gradual, it would be permissible to repeat a smaller repertoire of chant to permit the people a more gradual introduction to the singing of this music. The easy implementation would be to choose one Advent antiphon, for example, and employ different psalm verses on successive weeks. I wonder if anybody is attempting this as an alternative to choir-only implementation on Gregorian propers.
Also, norms for chant in the Mass already present in the introduction of the Graduale Romanum, are thus reexamined and amended, so that the function of each chant may be shown more clearly.