We find ourselves in something of a quandary this year about the concurrence of the fourth Sunday in Advent and Christmas Eve. My Sarum ordo by Dr William Renwick quotes the following from the Pie:
4th of Advent All of the Sunday until the 3rd. Nocturn exclusive. then all of the service of the Vigil. At Lauds mem. of Sunday with mass of Sunday in Chapter with the little hours as in the vigil without the Ps. Deus Deus meus respice etc.
That is for the Office. For the Mass in Chapter, it is of the Sunday. The last time this concurrence (Sunday 24th December in the Gregorian Calendar) happened was in 2000. We have this article in The Rad Trad – Vigilia Nativitatis: Nulla Fit Commemoratio?
For the Use of Sarum, Dr Renwick has this to say about the fourth Sunday in Advent:
In the earliest sources this Sunday was designated Dominica vacat and had no propers assigned to it. This would account for the variety of proper chants to be found amongst the Gregorian sources. Thus Sarum, in common with York, Rouen and the Dominicans has the Officium Memento while the Roman Missal repeats the Introit Rorate Celi from the previous Wednesday. However, the Ps. Peccavimus in the Sarum Use differs from that in the York, Rouen and Dominican Uses, which is Ps. Confitemini.
Where the Roman Use has the Offertory Ave Maria, the Sarum and Dominican Uses have Confortamini. This is a reversal of the previous Wednesday where the Roman Use has Confortamini and the Dominican and Sarum Uses have Ave Maria.
Officium. Memento nostri. Ps. 105:4-6. ad letandum is omitted.
In the Roman Use the Introit is Rorate celi, repeated from Wednesday in the Ember Days of Advent. Memento nostri appears ‘in the Transalpine regions’, László Dobszay, ‘The Proprium Missae of the Roman Rite’ Uwe Michael lang, Ed., The Genius of the Roman Rite (Chicago: Hillenbrand Books, 2010): 86.
Prayer. Excita quesumus Domine potentiam tuam
The York Use omits quesumus.
69
Epistle. Phil 4:4-7
In the Roman Missal the Epistle is 1 Cor. 4:1-5. In the Roman Missal the Epistle Phil. 4:4-7 appears on Advent 3.
Gradual. Prope est. This Gradual is repeated from Wednesday in the Ember Days of Advent.
Alleluya. V. Veni Domine et noli tardare.
The text is also found in Responsory 7 of the Third Sunday in Advent.
70
Sequence. Jubilemus omnes una. 11th c.
Anon. Translation © 2015 by Matthew Carver. Used with permission.
Roger Sorrell, St. Francis of Assisi and Nature : Tradition and Innovation in Western Christian Attitudes toward the Environment (Oxford: Oxford University Press, 1988):105 discusses the possible influence of this sequence on Francis of Assisi’s Il cantico di Frate Sole. This was also noted by Samuel W. Duffield in Latin Hymn-Writers and their Hymns (New York: Funk and Wagnalls, 1899):393.
The opening notes of the melody clearly reflect the opening pitches of the Alleluya.
71
Gospel. John 1:19-28
In the Roman Missal the Gospel, Luke 3:1-6, is repeated from the previous day.
72
Offertory. Confortamini. After Is. 35:4,5.
The Dominican and Hereford Uses also have the Offertory Confortamini here. The Roman and York Uses have Ave Maria. This is the opposite of the case on Wednesday in the Ember Days of Advent.
73
Secret. Sacrificiis presentibus quesumus Domine
Communion. Ecce virgo concipiet. Is. 7:14.
This Communion is repeated from Wednesday in the Ember Days of Advent.
Postcommunion. Populum tuum quesumus Domine donoroum tuorum
The Roman, York and Hereford Uses have the Postcommunion Sumptis muneribus quesumus Domine.
The Sarum Postcommunion also appears in the Westminster Missal.
What is interesting is the complete divergence between the Roman resumption of the Rorate Mass from Ember Wednesday on this Sunday and the alternatives from the French traditions. In the pre-1962 Roman rite, the solution would be to celebrate the Vigil of Christmas and commemorate the fourth Sunday of Advent. The Rad Trad article has a comment by Paul (I assume Paul Cavendish) affirming that this memory of the fourth Sunday of Advent was not an innovation of Pius X.
In the Sarum missal, the rubric is as follows in the Christmas Eve Mass:
If this Vigil occur on a Sunday, the mass of the Sunday is said in chapter ; and then there shall be a memory of saint Mary, and of All Saints only. But the mass of the Vigil is to he said at the high altar without any memory, with this Alleluya.
V. To-morrow the iniquity of the earth shall be blotted out, and the Saviour of the world shall reign over us.
It would seem logical not to commemorate the Sunday, given that the Sunday proper is recent in the diverging traditions. The Sarum solution is to celebrate two distinct masses on distinct altars, one in capitulo and the Vigil Mass at the high altar. It often happens that there is no memory when the displaced Mass is said on another altar by another priest. In a church where there is only one priest and one Mass on that day (without considering the Mass at the crowing of the cockerel which is in reality on Christmas Day), it might seem reasonable to commemorate the Sunday collect, secret and postcommunion prayers. That is what I am going to do.
The Blue Flower 
it might seem reasonable to commemorate the Sunday collect, secret and postcommunion prayers. That is what I am going to do.
That sounds eminently reasonable. Someone else might adopt the other option, and that would be reasonable too. Liturgy seems the richer for the diversity of the prayers available and its accommodation of different sensibilities.
Obviously it isn’t going to be the end of the world if it is done one way or another. Adrian Fortescue is quoted as having said “Such increased definiteness was bound to come in, after all, you must incense an altar somehow; it does not hurt to be told how to do so“. I think we should try to be as correct as possible, even though we are confident that God will forgive us if we make mistakes! Sloppiness is just as much an excess as Pharisaical rubricism!
Thank you for this!
I don’t remember how much attention I paid in 2000, but I’ve been wondering about this concurrence, though not with such thoughtful attention to detail!
This reminds me how the things work in the Byzantine rite. In a normal circumstance, the Byzantine rite has a vigil Mass (of course, combined with first evensong) on the evening of the 24th December, «at the eighth hour of the day» (4 pm), with the OT prophecies, and with the long and beautiful anaphora of Saint Basil; on Xmas morning, however, the Mass is “usual”, with propers of Xmas.
However, in a circumstance as this, things change. On the 24th December, the vigil Mass is said after tierce, with no propers, no OT readings, with regular anaphora of Saint John, and the solemn hours of the vigil are sung, but nothing of the Sunday (except resurrection antiphons in the office), and nothing of the Advent-tide. And the first evensong of Xmas without Mass, because there can only be one Mass per one astronomic day. On the morrow, the Xmas Mass is said with the propers, and with Saint Basil’s anaphora.
In short, in a case like this, the Byzantine rite observes the ranks like this: Xmas vigil greater than the Advent-tide; but lesser than in ordinary occasions (when the vigil Mass begins the Xmas-tide).
Before Charlemagne, in nowadays France the Advent had 6 weeks, and in a circumstance like this year, they would have begun the Advent-tide on the 12th November, and then have the last Sunday of Advent the 17th December; therefore, the 24th December they would have sung everything of the vigil. In short: move the Advent-tide one week backwards (earlier), so that the vigil won’t have concurrence with the last Sunday of the Advent-tide.
However, I am wondering about something else. What do you do with the ember days, when Xmas day falls on a Sunday? (Like last year, or in 2022.) The “normal” answer is that the ember Saturday would fall just one week before the vigil. However, as the Winter ember days are constructed as a parallel of the Easter triduum, my guess is that in such a year, the ember Saturday must supersede the Xmas vigil. When we look to all the Eastern rites, we can see how the ember Saturday in Winter is, in fact, a correspondence of the Xmas (or Theophany) vigil in those rites. Or, let me put it like this: why, in our recent Western books, is there such a discrepancy between what is assigned to the 24th of December Mass (short, no OT readings), and, on the other side, the Easter vigil or the Pentecost vigil?
Interestingly in the Lippe edition of MR1474 when the Nativity falls on a Monday the fourth Sunday is celebrated on the preceding day and the Vigil replaces the Ember Saturday. My educated guess would be that at one time the arrangement for Conventual Mass in the Roman rite would have been the same as in Sarum. It is surely a principle of liturgical conservatism to add things in, or at least retain them, rather than to omit them.