What is a Concelebrant minor?? They aren’t actually concelebrating. They are attending mass in choir dress.
Those priests participating in the mass but not at the altar. Pretty much only happens at diocesan and pan-diocesan events. It’s one of a dozen different terms used for those priests, whose role in such liturgies is minor.
Choir dress was seen much more often under the Trent to 1965 Roman missals, because under the those missals, only 3 persons vested, the principal celebrant as priest, the concelebrant or deacon as deacon, and a concelebrant, deacon, or subdeacon as subdeacon; all others literally sat in the choir area, and observed, mostly passively, the mass go on. Each did the part of they whose vestments they wore. If there were not enough clerics to fill the roles, the celebrant took those parts as well.
But post-Vatican II, the Roman Church renewed a tradition that the Eastern Rites have always maintained: priestly concelebration. The principle Celebrant has certain specific parts; many other parts may be handed off to concelebrant priests (such would be the concelebrants major); further, if there are concelebrant priests but no deacon, the deacon’s parts and tasks devolve upon a concelebrant (the current missal no longer has subdeacon’s parts). Such parts are usually marked clearly in the sacramentary. Additional concelebrants take the normal responses, and join in the words of institution (whispering them).
It’s a different understanding of the role of additional priests, and thus they should be vested.
Based upon the GIRM, The principle celebrant must be vested in alb, stole, and chasuble (and should have amice or hood, and a cincture, as well). As many other celebrants as can be vest likewise; then as many more in Alb, amice, cincture and stole. Then, and only then, as many more as may be present in Cassock and Surplice.
The times Cassock, Surplice and Stole are appropriate at present include:
Graveside services
Confessions
Communion outside the Mass*
Liturgy of the Hours as public liturgy***
Marriage outside the Mass
Public convalidation outside the mass
Baptism away from the chapel**
Extreme Unction
- Alb and Stole is more suitable by some of the theologians I’ve read and/or talked to.
** Usually, this means an emergency baptism… a child on life support equipment, or otherwise unable to be brought to the chapel of the parish.
*** Alb and Stole is commonly used, especially when mass will follow.