From a reader:
Compline ends with a Marian antiphon, as you know. For the Advent and Christmas seasons, the proper antiphon is the "Alma Redemptoris Mater." After that, you pick up the "Ave Regina Caelorum" through Lent. This is true in both the ordinary and extraordinary forms of the office.
Here’s the problem–in the older calendar, Christmas season ends on February 2nd (Candlemas). In the new calendar, it ends on the Solemnity of the Baptism of the Lord. The latter always comes before the former, usually in mid-January.
What Marian antiphon should be used by someone praying the ordinary form of the office for the period between the Solemnity of the Baptism of the Lord and Candlemas?
If it’s the "Alma…" that would seem to contradict the new end of Christmas season. If it’s the "Ave…" that would seem to be a rupture with tradition. Which one wins?
The rubric at the end of Compline says:
Deinde dicitur una ex antiphonis Beatae Mariae Virginae … Thereafter there is said one of the antiphons of the Blessed Virgin Mary.
You can freely choose which one you would care to say at the end of the newer form of the office. In that case you can freely choose to stick to the antiphon traditionally sung according to the older form of the office.