The wickedest of thoughts came into my mind ...
In England this year, as far as the 'Extraordinary Form' is concerned, Saturday August 15 is the Assumption and we are also allowed an External Solemnity on the Sunday August 16 (I wonder what S Joachim has to say about this).
What would be completely wrong for all celebrants to do, even old gentlemen in retirement celebrating privately in their homes, would be the following: to celebrate the old S Pius V Assumption Mass Gaudeamus on Saturday the 15th, and the Papa Pacelli Assumption Mass Signum magnum on the Sunday.
Oh, the iniquity of it. Keep this under your hats. We don't want the idea getting around.
Atcherlee it wouldn't be quite as simple as that. Gaudeamus exists in two forms. There is the S Pius V form of the Mass, using the lovely collect Famulorum tuorum, asking that we may be saved by the intercession of the Theotokos. This harks back to the early Christian idea that, as the Secret at the Vigil puts it, the very reason (idcirco ...) for the Assumption was that Mary might intercede for us.
But there is also the form of Gaudeamus found in the Sarum Missal ... which means that it was probably used over most of Northern Europe. The main difference here is that the Collect is not Famulorum tuorum, but a formula beginning Veneranda. In fact, before Sarum it was used in the Leofric Missal (or rather, Pontifical), the most recent editor of which has mooted the probability that much of its content goes back to the liturgical books brought to Canterbury by S Augustine. The collect goes
Veneranda nobis, Domine, huius diei festivitas opem conferat sempiternam, in qua sancta Dei genetrix mortem subiit temporalem; nec tamen mortis nexibus deprimi potuit, quae filium tuum Dominum nostrum de se genuit incarnatum. Qui tecum. (Lord, may the worshipful festivity of this day bring us everlasting assistance, on which the holy Mother of God underwent temporal death; but she could not be held down by the bonds of death since she brought forth Incarnate from herself thy Son our Lord.)
A final fact about that very stately collect: When Pius XII defined the dogma of the Bodily Assumption, he quoted it ... Yes! Verbatim! ... in the earlier part of the Bull Munificentissimus Deus. And he described it as 'praeclarum', further accentuating its Magisterial significance by telling us that "Decessor noster immortalis memoriae Hadrianus Primus misit [the Sacramentary containing it] ad Imperatorem Carolum Magnum".
After the Definition, a new Mass, Signum magnum, was imposed on the Latin Church. It was scraped even cleaner of Tradition than were the Holy Week services which Pius XII also sponsored in the 1950s. Why was the very suitable collect Veneranda not given some role in this composition?
Since Hannibal Bugnini is no longer alive to enlighten you, his mantle falls upon my unworthy shoulders.
Pius XII was anxious to leave open the question of whether our Lady did, or did not, "undergo a temporal death" before her Glorious Assumption.