Well last year the consensus on All Saints Day (a Saturday) was that the Saturday evening Mass should be for All Saints, the Sunday for All Souls. So it is probably the same situation.
Aug 14 evening: Vigil of Assumption
61. If the same day were to call for celebration of evening prayer of that day’s office and evening prayer I of the following day, evening prayer of the day with the higher rank in the Table of Liturgical Days takes precedence; in cases of equal rank, evening prayer of the actual day takes precedence.
A person who assists at a Mass celebrated anywhere in a Catholic rite either on the feast day itself or in the evening of the preceding day satisfies the obligation of participating in the Mass.
the universal law of the Roman Rite takes precedence over all others.
3. Each and every day is sanctified by the liturgical celebrations of the People of God, especially by the Eucharistic Sacrifice and the Divine Office.
The liturgical day runs from midnight to midnight. However, the celebration of Sunday and of Solemnities begins already on the evening of the previous day.
60. If several celebrations fall on the same day [I assume this means calendar day], the one that holds the highest rank according to the Table of Liturgical Days is observed.
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