In a discussion on the Liturgy List, Pr. Vieker helpfully pointed out a very little observed footnote in LSB on page xi. On that page are listed out Feasts and Festivals. But which is which? The bolded items are denoted as "principal feasts of Christ" and are "normally observed when they occur on a Sunday." What are these?
Eve of the Circumcision and Name of Jesus (Dec. 31)
Circumcision and Name of Jesus (Jan. 1)
Purification of Mary and the Presentation of Our Lord (Feb. 2)
Annunciation of our Lord (March 25)
The Nativity of St. John the Baptist (June 24)
The Visitation (July 2)
St. Michael and All Angels (September 29)
All Saints Day (November 1)
All these are FEASTS in LSB and the lectionary introduces them so. The rest of the days on that page are festivals "that may be observed according to local custom and preference." A quite separate category are Commemorations. Commemorations lack propers and so are not intended to be "celebrated" in the Divine Service, but the person (or event) commemorated may be included in the prayers for that day.