Rigidity, inflexibility, is the hallmark of the Bugnini, post-Conciliar, liturgical Calendar.
Let me explain what I mean. Today is The Second Sunday of Advent. I'm glad. We get the third collect in that wonderful sequence of Excita collects; 'Stir up' is what we pray because we know that our indolence and our Sin call for a rude shake up. (If I were the Holy Father, I would speak about the fact that we are all Laodiceans, which would sort out the Men who had read Apocalypse 3:15sqq. from the Boys who hadn't.) Today's collect in the Vetus Ordo could serve beautifully as the rallying prayer of the New Evangelisation. Heaven forbid that we should lose this Sunday collect.
But today is also the Feast of our Immaculate Lady's Conception. And this feast comes below a Sunday in Advent in the Bugnini Order of Precedence which (forgive me for going on about this, and for the horrible pun) precedes the Council (I have a 1957 ORDO, pontificate of Pius XII, beside me which proves this!). So ... Hard Cheddar ... the Festival gets transferred to Monday. Which is undoubtedly better than completely ignoring it. But there's not a tiniest mention of it in the Sunday Mass. This is the same rubrical problem which I raised in my piece for S Andrew's Day. (You may be surprised to learn that the Church of England's Liturgical Commission, when publishing extensive propers for this feast in 1991, commented on how appropriate they were to the season of Advent. Indeed so. Mary is hardly a person to be ashamed to mention in Advent, even if she is destined to get a bit of a plug in the Novus propers of Advent IV.)
Is there another solution? In the Byzantine Rite, when two celebrations coincide, parts from each are often combined. The attitude behind this is not unknown in Anglicanism, where there were for centuries no rules at all about the problems of Occurrence and Concurrence. So there survive Tractarian sermons for 1842 and 1853, when Good Friday occurred on March 25, combining the themes of the Annunciation with those of Good Friday; a splendid opportunity, indeed, for thinking about the Co-Redemptrix*, the Compliant New Eve, at the foot of the Cross of the Obedient New Adam.
The older Tradition of Latin Christendom provides the neatest answer. It relies upon the simple concept of "Commemoration". So, in the Saint Lawrence Press ORDO on my desk, giving the Roman Rite according to the rules of 1939, Our Lady's Feast occupies the day. (The blog Rorate has reminded us that the Rubrics of 1960, happily, reverted to this traditional, pre-Pius XII, arrangement, although, in less than a decade, the Novus Ordo dragged us back to Pius XII). But there is a commemoration of the Sunday; which means that its Collect, Secret, and Postcommunion are said after those of our Lady. And in the pre-Pius XII rite, on such occasions as this, the Sunday Gospel is read as the Last Gospel at the end of Mass, rather than the Johannine Prologue ... after all, Vatican II did call for a Richer Table of the Word of God ... so why is it so unspeakably dreadful to have two Gospels on a Sunday?.
I prefer the flexible and Common Sense instincts at work here, backed by the authority of Pius XI and B John XXIII, to the rigid winner-takes-all system backed by Pius XII and Paul VI.
*As the (2005) Anglican-Roman Catholic agreement on Mary puts it, "The New Eve shares in the New Adam's victory over sin and death".