Pius XII made those changes by the decree "Cum nostra hac aetate" of 23 March 1955.
However, a few sedevacantists do observe the revisions beginning in 1955, while excluding those of the John XXIII, such as the Congregation of Mary Immaculate Queen[6][7].
The celebrations including the revisions according to General Roman Calendar of Pope Pius XII starting in 1955 are listed here below.
The days within the Easter and Pentecost octaves were raised to the Double rite, had precedence over all feasts, and did not admit commemorations.
On 13 January the Commemoration of the Baptism of our Lord was to be celebrated in the major double rite, using for the Office and the Mass those previously said on the Octave of the Epiphany.
But if 13 January occurred on Sunday, the Office and Mass were to be those of the "Feast of the Holy Family" without any commemoration of the Baptism of Our Lord.
The days of the suppressed Octaves of Corpus Christi and the Most Sacred Heart of Jesus became feriae per annum.
Although not listed on the general Calendar, a commemoration of St. Anastasia Martyr is made at the second Mass on Christmas Day.
The rule has since the Middle Ages been phrased as "Easter is observed on the Sunday after the first full moon on or after the day of the vernal equinox."