Ttony of The Muniment Room has a regular feature in which he reproduces the current list of celebrations, or Ordo for the current week of the pre-1910 calendar; this was the the liturgical calendar before the major reforms of Pope Pius XII in the document Cum nostra hac aetate of 1955. Over the weeks, it is fascinating to see how many extra prayers for saints, or “commemorations” there used to be. Here is the Ordo for the week beginning Saturday 10 August, a relatively quiet week:
Note for example, that on Tuesday the Mass of the day was the celebration of the day within the Octave of the feast of St Lawrence which had been celebrated on the 10th of August. Then for the collect, the secret and the postcommunion, there was a second prayer for the feast of Saints Hippolytus and Cassian, Martyrs. Then there was the prayer Concede, a prayer in honour of Our Lady so that there was a third prayer to make up the number of prayers which was usually an odd number. (“The indulgence begins” is fascinating, but not to the point here – see this post from Ttony again for an explanation.)
The rules were not straightforward, but any priest was able to refer to the local diocesan or religious Ordo (the detailed liturgical calendar for his diocese or order) and check which prayers were to be said on any particular day. Some clergy and MCs were experts at all the rules, while most got to know their way around to some degree. What routinely happened was that a feast that was “outranked” by the feast of the day was commemorated, and depending on the rubrics of the time, there is often a commemoration of the Church, the Pope, and so on.