358. In the Lectionary for weekdays, readings are provided for each day of every week throughout the entire course of the year; hence, these readings will in general be used on the days to which they are assigned, unless there occurs a Solemnity, a Feast, or Memorial that has its own New Testament readings, that is to say, readings in which mention is made of the Saint being celebrated.
Should, however, the continuous reading during the week from time to time be interrupted, on account of some Solemnity or Feast, or some particular celebration, then the Priest shall be permitted, bearing in mind the scheme of readings for the entire week, either to combine parts omitted with other readings or to decide which readings are to be given preference over others.
This option, to combine texts or to make choices on priorities, presumes a priest is watchful over several days of Lectionary activity. It seems to place a priority of the pastoral and spiritual needs of a particular community above the virtue of a unified Lectionary proclaimed “the same” from place to place.
In Masses for special groups, the Priest shall be allowed to choose texts more particularly suited to the particular celebration, provided they are taken from the texts of an approved Lectionary.
For special groups, I would presume communities that are not celebrating Mass on a daily basis. Possibly pilgrimages, retreats, and events like that.
359. In addition, in the Lectionary a special selection of texts from Sacred Scripture is given for Ritual Masses into which certain Sacraments or Sacramentals are incorporated, or for Masses that are celebrated for certain needs.
Sets of readings of this kind have been so prescribed so that through a more apt hearing of the Word of God the faithful may be led to a fuller understanding of the mystery in which they are participating, and may be educated to a more ardent love of the Word of God.
Therefore, the texts proclaimed in the celebration are to be chosen keeping in mind both an appropriate pastoral reason and the options allowed in this matter.
None of these prescriptions is much changed from the 1975 edition of the GIRM. All of these options have been in place for two generations. Anybody see anything worthy of comment?