Another document of 3 December 1972 introduced changes to the Roman Missal because of the Motu Proprio MINISTERIA QUEADAM.
It included: “… Accordingly, the order of subdiaconate will no longer exist in the Latin Church. A reader or acolyte, even one not formally instituted, will perform the subdeacon’s functions. … The function of the subdeacon, then, is completely suppressed. …
In the General Instruction of the Roman Missal, therefore, everything about the subdeacon has to be deleted and the text in certain parts amplified or emended to correspond to the new discipline.”
(Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, pages 463-464)
This presentation concludes that it was approved by Pope Paul VI on 22 December 1972.
A change in the Roman Missal, is in n. 301:
1970 GIRM: “301. The subdeacon wears the tunic, which is put on over the alb.”
Variation of 1972: Deleted 301.
1975 GIRM: “301. Ministers below the order of deacon may wear the alb or other vestment that is lawfully approved in each region.”
(Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, page 524).
Has the tunic been “lawfully approved” anywhere? Not to my knowledge.
The Instuction on Certain Questions … at
vatican.va/roman_curia/pontifical_councils/laity/documents/rc_con_interdic_doc_15081997_en.html includes in Article 6 §2:
“In the same way, the use of sacred vestments which are reserved to priests or deacons (stoles, chasubles or dalmatics) at liturgical ceremonies by non-ordained members of the faithful is clearly unlawful.”
Can a tunic be distinguished from a dalmatic? It sounds difficult, according to the 1910 Catholic Encyclopedia at
newadvent.org/cathen/15087a.htm :
“… By tunic (tunicella) is understood in liturgical language that sacerdotal upper vestment of the subdeacon which corresponds to the dalmatic of the deacon. According to present usage the dalmatic and tunic are alike both as regards form and ornamentation. They also agree in the manner of use as well as in the fact that the tunic, like the dalmatic, is one of the essential vestments worn at the pontifical Mass by the bishop. It is unneccesary here to go into full details, but it will suffice in regard to form, ornamentation, and use to refer to what is said under dalmatic. As regards the form, according to the directions of the “Cæremoniale Episcoporum”, the tunic should be distinguished from the dalmatic by narrower sleeves, but this is hardly observed even in the pontifical tunic, which is worn under the dalmatic. …”.