Q: There are THREE celebrations of anniversaries of dedications of four Roman Basilicas.
1) August 5 of Mary Major (Euchology and Readings from Masses for BVM)
2) November 9 of John Lateran (Euchology and Lectionary Readings are from anniversary of dedication of Church [outside the dedicated church])
3) November 18 of Peter at Vatican and Paul outside the Walls (together) [Euchology and Readings from Common of the Apostles]
Is there a reason why #1 and #3 do not use the (Euchology and Lectionary Readings are from anniversary of dedication of Church [outside the dedicated church])
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A: Indeed, there is a reason. The Lateran is not just a basilica. It is the cathedral of Rome, and therefore the mother cathedral of all cathedrals and parishes around the world.
So each year a parish celebrates the solemnity of the anniversary of the dedication of its own church building, the feast of the dedication of its diocesan cathedral, and the feast of the Lateran basilica.
Observing the other three Roman basilicas is optional.
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Q: Got it…
I guess I was more interested in the issue of the dedication anniversary of the other three (while being optional, indeed) does not use dedication texts but sanctoral? It seems (to me) that the anniversaries of dedications of these basilicas are not the same as observances of Mary and of the saints who are observed on several other days.
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A: I see. The calendar has some funny quirks to it. I believe that the day assigned to honor the Presentation of Mary (November 21) was chosen to coincide with the dedication of the church of St. Mary in Jerusalem. So the other dates in your question are more celebrations of what the churches represent than their actually dedication anniversaries. An anniversary of a church would normally be celebrated either as a solemnity or a feast, and those two dates are neither, so they had to come up with something.