Here are some documents I’ve found.
Inter oecumenici
Instruction on implementing liturgical norms
Consilium (of Sacred Congregation of Rites) - September 26, 1964
adoremus.org/Interoecumenici.html
With this gem
- The Holy See alone can grant permission for use of the vernacular in those parts of the Mass that the celebrant sings or recites alone.
- Pastors shall carefully see to it that the Christian faithful, especially members of lay religious institutes, also know how to recite or sing together in Latin, mainly with simple melodies, the parts of the Ordinary of the Mass proper to them.
To be fair, this document allowed much more vernacular than was alluded to in SC. However, 59 seems to be almost universally ignored by the hierarchy.
- The choir and organ shall occupy a place clearly showing that the singers and the organist form part of the united community of the faithful and allowing them best to fulfill their part in the liturgy.
In other words, no longer in the back of the church? This statement seems contradictory to me. The choir is supposed to be a big part of the liturgy, no doubt, but they are not supposed to be the focus. Why then, would you want them to have more of a presence, which would naturally lead to more focus on them?
APOSTOLIC CONSTITUTION
ISSUED BY HIS HOLINESS POPE PAUL VI
MISSALE ROMANUM
ON NEW ROMAN MISSAL
vatican.va/holy_father/paul_vi/apost_constitutions/documents/hf_p-vi_apc_19690403_missale-romanum_en.html
We are fully confident that both priests and faithful will prepare their hearts more devoutly and together at the Lord’s Supper, meditating more profoundly on Sacred Scripture, and at the same time they will nourish themselves more day by day with the words of the Lord. It will follow then that according to the wishes of the Second Vatican Council, Sacred Scripture will be at the same time a perpetual source of spiritual life, an instrument of prime value for transmitting Christian doctrine and finally the center of all theology.
You can sense an excitement over these reforms that great changes were going to occur. I wonder how they felt a few years later?
And I also notice a continued emphasis on the ancient sources, a seeming longing for that before medieval developments. This would appear to be a large discord from what Pope Benedict says about not ignoring medieval developments in favor of the ancient. He says we should value all, but not forego more recent developments in complete favor of the ancient.
In all, I can see a source of confusion over these documents. The GIRM, at least, is much more rigorous, but I can see some merit in the argument that much of the problem stems from how vague these documents are.