I live in Greater Sydney in Australia and my experience of Gregorian chant is largely filtered by more knowledgeable people who lead the choirs in the Latin Mass apostolates there. Lewisham is a suburb in the city where a group of Latin Mass enthusiasts began a regular Latin Mass in a disused hospital chapel back in 1988 or thereabouts. As far as I know, they have always sung the Monastic Sub Tuum Praesidium at the end of Mass. This practice has spread west to the Sunday sung Mass in Blacktown. The usual sound is the entire congregation joining in with the organ for a very rousing rendition. It’s very memorable.
So, when I put together my course teaching people to Sing the Little Office of the Blessed Virgin Mary, I sang the Monastic Sub Tuum for Compline. The rest of the course uses the Vatican or Roman chant. Mostly. And I was aware of the difference, but went ahead anyway because if you’re singing the Little Office with me, we’re going to use the Monastic Sub Tuum.
I’m not alone. Back in 1632 when Pope Urban VIII was pushing through changes to the Roman Breviary, many religious orders held on to the old books.
Claiming the privilege of exemption granted by Pope Pius V because of the antiquity of their own Breviaries, the Dominicans, Benedictines, Cistercians, and Carthusians refused to adopt the revisions. Moreover, the revisions were never accepted at St. Peter's or the Lateran in Rome itself! This produced two distinct versions of the Latin hymnal that were to coexist for more than three hundred years. - Preces Latinae, Michael Martin
As I understand it, the old books are represented in the Antiphonale Monasticum and the new books in the Antiphonale Romanum. The articles about Pope Urban’s reform stress the multitudinous changes to the text. I’m not sure if he stipulated the changes in melody as well. Let me know if you can enlighten me on that point.
So, here is the Monastic Sub Tuum:
and here is the Roman or Vatican Sub Tuum:
You can see the first two lines of both are pretty much identical. The Vatican version doesn’t include rhythmic markings, but allows for similar rhythmic interpretations. The remaining two lines are also very similar, following the same general shape, finishing with the same pattern for “benedicta.”
Closing, local variations in singing are unavoidable. I wouldn’t expect different families to sing Compline in identical ways. When groups come together to sing, then it’s good to be aware of the differences and agree on a common way to sing together. This happens in all musical genres, so it makes sense that chant would also need to accomodate local variations. I would argue that chant gives a more uniform base than other church music. The variations in vernacular hymns are much more thorny than the differences here in the this Marian Antiphon.
To finish off, here are the Cistercian …
… and the Dominican:
Keep praising God! Blessed be God and blessed be Mary, Virgin and Mother!