Via the New Liturgical Movement blog, I've been made aware of the current standards imposed on guest choirs when singing at Saint Peter's Basilica at the Vatican.

If you click here, you can access the document in full.

Many of the points therein, which were unimaginable under the John Paul II reign, are now just common sense; for example, the point which states that "Gregorian chant has first place". It's such a relief to now that that's a no-brainer.

Of particular interest was the list which stipulates which settings of the Ordinary are to be used, based on the season or feast. Most Latin-using churches are only aware of Mass VIII, aka the Missa de Angelis. But it's so sing-songy and late in composition that some argue it's not even real Gregorian chant; it's certainly not medieval in any case.

Sundays of Advent: Missa XVII Credo IV
Sundays of Christmas: Missa IX Credo IV
Sundays of Lent: Missa XVII Credo IV
Sundays of Easter: Missa I Credo III
Sundays of Ordinary Time: Missa XI Credo I
Feasts of Ordinary Time: Missa VIII Credo III
Feasts of the B.V. Mary: Missa IX Credo IV
Feasts of the Apostles: Missa IV Credo III

I really hope my parish implements this for our Latin Mass. I don't know how everyone couldn't be sick of the same old Gloria and Credo every single time. The Vatican Kyriale has 18 or so different options for the former, and 4 for the latter.