In the letter with this Motu Proprio of 7 July 2007 it has "I would like to draw attention to the fact that this Missal was never juridically abrogated and, consequently, in principle, was always permitted. At the time of the introduction of the new Missal, it did not seem necessary to issue specific norms for the possible use of the earlier Missal. Probably it was thought that it would be a matter of a few individual cases which would be resolved, case by case, on the local level. "
Similarly in the Motu Proprio itself, from an unofficial translation:
"It is, therefore, permissible to celebrate the Sacrifice of the Mass following the typical edition of the Roman Missal promulgated by Bl. John XXIII in 1962 and never abrogated, as an extraordinary form of the Liturgy of the Church."
Some documents about the possible use of the earlier Missal:
Instruction Constitutione Apostolica of 20 October 1969:
"14. The individual conferences of bishops are to decide on the date when the texts of the new Roman Missal are to become obligatory, except for the cases that are specified in this Instruction nos. 20-21. It is better that such a date be no later than 28 November 1971 ...
19. Elderly priests who celebrate Mass without a congregation and who might encounter serious difficulty in taking up the new Order of Mass and the new texts of the Roman Missal and Lectionary for Mass, may, with the consent of their Ordinary, keep to the rites and texts now in use.
20. Special cases of priests who are infirm, ill, or otherwise disabled are to be submitted to this Congregation.
Pope Paul VI approved this Instruction on 18 October 1969 and ordered its publication for the exact observance of all concerned."
(From Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, pages 536 - 537).
Sacred Congregation of Divine Worship, Notification "Instructione de Constitution" of 14 June 1971:
"... 1. THE MISSALE ROMANUM AND THE LITURGIA HORARUM
1. In celebrations in Latin use of the Missale Romanum and the Lectionarium Missae published by this Congregation is already authorized. The Liturgia Horarum may be used as soon as the books have been published.
2. The conferences of bishops are to see to completion as soon as possible of the translation and publication of these books in the vernacular.
With due regard for special problems attendant on these projects, the conferences should, however, settle on a definite date when translations, having their own approval and the Apostolic See's confirmation, may or must be put to use in whole or in part.
From the date on which the translated texts become obligatory for celebrations in the vernacular only the revised form of the Mass and the liturgy of the hours will be allowed, even for those who continue to use Latin.
3. Continued use, in whole or in part, of the Missale Romanum in the 1962 editio typica, as emended by the 1965 and 1967 decrees and of the Breviarium Romanum formerly in use is allowed, with the consent of the Ordinary and only in celebrations without a congregation, for all those who because of their advanced years or illness find serious difficulties in using the New Order of Mass in the Roman Missal, the Lectionary for Mass, or the book of the liturgy of the hours. ..."
(From Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, page 545).
Sacred Congregation of Divine Worship, Notification "Conferentiarium Episcopalium, on the obligatory nature of the Roman Missal of Paul VI" of 28 October 1972:
"The responsibilities of the conferences of bishops to see to the preparation of translations of the liturgical books and the required petition for their confirmation by the Apostolic See have already been specified, with the approval of Pope Paul VI, by this Congregation through its notification of 14 June 1971. [footnote a: See Sacred Congregation of Divine Worship, Notification "Instructione de Constitution" of 14 June 1971, n. 2 and 4]
Throughout the world the conferences have been in the process of carrying out these responsibilites, with the result that as sufficient time has passed the word is all but complete. When a conference of bishops decrees that the translation of the Roman Missal, or any part of it, for example, the Order of Mass, is obligatory in a region, Mass, whether in Latin or the vernacular, may be celebrated lawfully only according to the rite of the Roman Missal promulgated 3 April 1969 by authority of Pope Paul VI.
As to the rules issued by this Congregation in favor or priests who because of their advanced years or infirmity find serious difficulties in using the new Order of Mass in the Roman Missal or the Lectionary for Mass, it is clear than an Ordinary has the power to grant them permission to use, in whole or in part, the Missale Romanum in the edito typica of 1962, as emended by the decrees of 1965 and 1967, but only for celebration without a congregation. [footnote d: Sacred Congregation of Divine Worship, Notification "Instructione de Constitution" of 14 June 1971, n. 3] Ordinaries cannot grant this permission for the celebration of Mass with a congregation. Both local and religious Ordinaries must rather see to it -- without prejudice to non-Roman liturgical rites lawfully recognized by the Church but with no exception based on the claim of any, even immemorial custom -- that all priests and people of the Roman Rite duly accept the Order of Mass in the Roman Missal; that through greater study and reverence they come to appreciate it for the treasures of both the word of God and of liturgical and pastoral teaching that it contains."
(From Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, page 549).
Letter from the Secretariat of State, Cardinal J. Villot to Bishop R. Coffy, President of the liturgical commission of France, 11 October 1975. (Published in Notitiae 12 (1976) pages 81-83:
"... Through the Constitution Missale Romanum Pope Paul, as you know, orders that the new Missal is to replace the former one, notwithstanding any constitutions or apostolic ordinances of his predecessors -- including, therefore, all the determinations of the Constitution Quo primum. No one, in France or anywhere else, can therefore claim an indult granted by Quo primum and allowing use of the former Missal. This can be used exclusively in the case envisioned by the notification of the Congregation for Divine Worship, 14 June 1971, approved by Pope Paul. The notificatin of 28 October 1974 made it explicit once again that Ordinaries do not have the power to grant this permission (to use the former Order of Mass) for celebration with a congregation ... notwithstanding any custom, even one from time immemorial. ...".
(From Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, page 550).
By J.R. Lilburne, 8 July 2007. I give what I have written on this page to the public domain.
Motu Proprio Summorum Pontificum unoffical translation
Letter with the 2007 Motu Proprio
1969 Apostolic Constitution Missale Romanum