On page 1721 of the Liber Usualis, I see the formal setting of the V & R "Laetamini in Domino" which is "sung as above only on the Feast itself". "On the other days, the ordinary tone is used."
Yes, the 1st Vespers is normally considered on the feast itself. This year it's a little trickier because the Eve is also Sunday.
For the traditional form (aka EF), October 31st is also Christ the King this year. For Sunday evening the 31st, the FSSP ordo specifies 2nd Vespers of Christ the King with a commemoration of All Saints. For the modern form (aka OF), I'm not so sure about the relative ranking of the Sunday and the Nov 1 solemnity. I suspect Sunday takes precedence, maybe someone else here knows for certain.
In the Table of the Liturgical Days at the beginning of the OF Liturgy of the Hours, "Solemnities of the Lord, the Blessed Virgin Mary, and saints listed in the general calendar, and All Souls Day" is ranked (at 3) above "Sundays of the Christmas season and Sundays in Ordinary Time" (at 6). So, my understanding is that in the OF 1st Vespers on Oct 31 2010 would be from All Saints.
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