So did you observe the Immaculate Conception yesterday, or are you enjoying it today?
When December 8 is a Sunday, the "EF" keeps the Festival on that Sunday (the Sunday being commemorated ... with, in the St Lawrence ORDO [have you got one yet?] Last Gospel of the Sunday). But in the Novus Ordo, the Sunday yesterday was undisturbed and the Solemnity is transferred to today, Monday. May the Theotokos, Kyria kai Despoina, amomos kai akhrantos, continue to pray for us all.
Since this Festival is not, at least in Britain, of Obligation, the Novus Ordo rule means that the great bulk of the congregation never experiences it. I think this is highly unfortunate. Even the Church of England can understand that this observance is (PHG) "appropriate to the season of Advent". And the 2005 ARCIC agreement between negotiators of the Catholic Church and of the Anglican Communion wrote "We affirm together ... that in view of her vocation to be the Mother of the Holy One, Christ's redeeming work reached 'back' in Mary to the depths of her being and to her earliest beginnings."
The idea that Sunday Masses ... especially in seasons such as Advent ... should not repeatedly be obscured by observances from the Sanctorale is, in itself and up to a point, Lord Copper, a sound principle. But if our Lady's Conception were observed on Sunday only when that Sunday was the 8th of December, this collision would happen (generally) once every six years. (There are no other Universal observances waiting to gang up on the Sundays of Advent ... I can guarantee that the Apostle S Thomas won't try it on.) Would the loss of just one Advent Sunday Mass out of 24 really be the end of the world as we know it?
[Byzantines, sensible people, allow more than one celebration to be combined in the Liturgy of a single day. The Tractarians even went so far as to preach on our Lady of Sorrows when Good Friday occurred on March 25! Few of the daft and rigid fads of the Novus Ordo are as plain silly as its grim-faced and unnatural phobia of 'Commemorations'. So Enlightenment! So Pistoia!]
Similar considerations apply to the occasions when a Festum ... such as the festival of one of the Apostles ... happens to flutter down on to one of the 'green' Sundays "per Annum" of 'Ordinary Time'. The Church of England wisely ... Yes!! ... permits either the Sunday observance or that of the Saint; decision, in a well-judged exercise of Subsidiarity, is left to the local clergy.
Cardinal Sarah once admirably attempted to bring the "EF" and "OF" calendars into line. That splendid hope was abandoned; it was indeed too ambitious given current sensitivities. But a change to the provisions in the OFalong the lines suggested here would be legislatively easy, and One Small Step in the direction of greater unity within the Roman Rite.