Section 20 of Liturgiam authenticam has this:

While it is permissible to arrange the wording, the syntax and the style in such a way as to prepare a flowing vernacular text suitable to the rhythm of popular prayer, the original text, insofar as possible, must be translated integrally and in the most exact manner, without omissions or additions in terms of their content, and without paraphrases or glosses. Any adaptation to the characteristics or the nature of the various vernacular languages is to be sober and discreet.

Repetition of the "Glory To God" takes the great hymn of the church and turns it into a Litany.

This puts emphasis on one part, the people end up only singing that part and that would appear to be in contravention of the intent that the Mass text be said unaltered.

Thanks for all the great links!

Maybe this is what is hiding from your memory:

It is strictly forbidden to change in any way the sung text, to alter or omit words, or to introduce inappropriate repetitions. This applies also to compositions of sacred polyphony, and modern sacred music: each word should be clearly, and distinctly audible.

Musica sacra (1958) 21.a

G: i would suggest the operative word is "inappropriate."

I think that care ought to be taken in criticizing or classifying repetitions as changing their very substance and meaning. As I recall, someone here (Aristotle?) advanced a very worthy arrangement, years back, of the Missa de Angelis "Gloria" that utilized the intonation phrase as a refrain, and which JT published and advocated as an "entry-level" method for congregational singing of the Latin text. What's good for the goose.....

i would suggest the operative word is "inappropriate."

Sorry, modifying what?

(Save the Liturgy, Save the World)

@G: see pius xii above

especially considering that the 9 kyries were originally cut down from several different litanies containing dozens of kyries each.

So we have, at least from the eighth century, our present practice of singing immediately after the Introit three times Kyrie Eleison, three times Christe Eleison, three times Kyrie Eleison, making NINE invocations altogether.

The most bone-headed change to the Ordinary following the Council, (IMO.)

Save the Liturgy, Save the World!

Re previous comment: Prior to V2 many Episcopalian parishes, at low mass, said a ninefold Kyrie responsively and nobody had a problem with it.

This was the standard, both sung and spoken until V2.

I think people seriously underestimate congregations all the time. If they were used to a ninefold kyrie, and knew when to go into the Christe eleison, they could do it. Have the schola/choir sing along with 'em... as long as you're not doing crazy polyphonic stuff, they'd be just fine.

In the Episcopal Hymnal 1940, Missa cum jubilo appears in English as the "Fourth Communion Service" with accompaniment by Healey Willan (not credited in the hymnal until The Hymnal 1982). The standard ninefold Kyrie structure is marked to alternate voices throughout, "Boys" starting, "Men" following, and "Full Choir" on the final Kyrie. But the implementation of that alternation varied from parish to parish; in many parishes, everyone sang all of it; in some parishes, it would be sung with one set of voices (trebles or men) on the first of each petition, the opposite voices on the second , and full on the third petition. In the parish in which I grew up, we (adult and children's choir both) learned to sing that mass setting in Greek and Latin by reading the words from a mimeographed sheet and attaching them to the correct 'note' or 'notes'. When I learned to sing chant directly from the Liber as an undergraduate (40 years ago), it was so enlightening and a joy to see the correct notation. (For instance, Willan grouped the opening six puncta of the Kyrie into 3+3 instead of 2+2+2, both with beams and the rhythm of his accompaniment.) When my present 'work church' congregation (Anglo-Catholic) sing this mass or Missa De Angelis (or any of the other Communion Services with the exception of the Oldroyd, where they wisely default to just the congregational part) they sing all of everything with great gusto, simply because they love traditional music, and "That's the way we've always done it". (I never thought I'd hear the "Seven Last Words of the Church" in the positive context!) My home parish celebrates the EF as the principal Mass, and those worshippers have learned to sing Missa De Angelis and Missa cum jubilo. (We don't sing the responsorial psalm at the English and Spanish NO masses, but when Father chants, the congregation sings the usual Ordinary and responses.)

Off-topic: They also sing along on the Anglican chant psalm every week (I only use ten tones, so they are familiar) and chant the responses and the Our Father. They are less solid on the responsorial psalms we use in the summers, but the consensus from parishioners seems to be that 1) the Anglican chants are easier to sing (and we do have a cappella verses, during which the congregation still sings); and 2) fewer people in the pews and in the choir makes everyone less confident. Several parishioners have picked up on the fact that I set the responsorial psalms to the same tone for anywhere from two to four weeks, and make the changing responses grow organically from the tone. (They are always plainsong, not metrical.)