The 1962 crowd at Rorate extol the centuries old rubric of the Christmas vigil Mass superseding the scheduled fourth Sunday of Advent (a shame we had the longest possible Advent last year and the shortest this year), without any commemoration of the Sunday. Are we to believe this is consonant with liturgical custom in the Roman rite? The Sunday is entirely disregarded on the grounds that it is already a feast of the Lord, making a commemoration redundant, according to the drastic reductions of Papa Roncalli. The problem is that the two are not exactly the same sort of day.
The vigil is, for one, a vigil. Prior to 1960 it was exceptional among major vigils in that it was celebrated in violet vestments without use of the folded chasuble (more along of the lines of vigils of the Apostles—axed in the '62 books, less like Pascha and Pentecost); also unusual were the combination of ferial Mattins and its one nocturne of lessons from Saint Jerome with festive Lauds, complete with doubled antiphons, reflecting a full celebration.
Advent's fourth Sunday is comparatively conventional and restrained. It is still a semi-double, which would ordinarily admit commemorations and, despite the festive Lauds normal to Sunday, it is still a somewhat penitential day, with folded chasubles, no organ music, and continuation of the Rorate caeli desuper texts from early Advent.
It seems improper to call either day full festive, but the vigil clearly anticipates Christ's birth while the Sunday looks forward with sober restraint. The latter is as integral to fulfilling Advent as the former is to ending it, and so omitting its memory makes Advent shorter than the natural calendar has already done.
Byzantine tradition has a commemoration system both simple and complex. At Vespers one simply adds the troparia from the superseded feast to those of the day; at the Divine Liturgy one tacks the tropar and kontakion onto those of the day. Orthros (Mattins) and its sessional hymns are where things get messy. The older Roman system similarly desires to accommodate as much of the liturgy as possible and does so in an easier manner, merely adding the orations at Mass, combining Mattins readings of the day so the concatenated lessons of the replaced feast Mass may be added, the versicles and oration at the major hours, and the Gospel read in place of Saint John at Mass. There are more places for commemorations, but they are easier to manage.
In light of this, the 1962 omission of the Advent Sunday, which is fundamentally a different day than the Christmas vigil, seems more consonant with.... the rubrics of 1970.... with the two days flipped....
Note: folded chasubles seem to be making an overdue comeback. Perhaps we are witnessing organic, rather than wholesale, restoration?