I have been reading more of Bugnini's verbose apologia, and two things strike me. One is that the agenda which the Consilium (Bugnini's team) produced and followed did not derive from the Council, but rather from pre-existing ideas, which also informed some of the ambiguous wording in Council documents and were thus given legitimacy; the second is that the whole project went a lot further and a lot faster than the Council Fathers or the Holy Father had intended, but that any attempts to stop it were futile.
The first of these struck me because of the priority given by the Consilium to communion under both kinds, and concelebration. So for example, Sacrosanctum Concilium says:
The dogmatic principles which were laid down by the Council of Trent remaining intact, communion under both kinds may be granted when the bishops think fit, not only to clerics and religious, but also to the laity, in cases to be determined by the Apostolic See, as, for instance, to the newly ordained in the Mass of their sacred ordination, to the newly professed in the Mass of their religious profession, and to the newly baptized in the Mass which follows their baptism. (SC §55)This clearly envisages that on very specific and defined occasions, the laity may receive Communion under both kinds. There is no action required of the Consilium in this regard. Yet an early priority was to study this issue, with a view to extending the provision. Why? I can only assume because that is what had already been desired (and indeed practiced, in disobedience) by some prior to the Council.
Concelebration was again to be practiced on a limited basis. It as the last issue dealt with in the Chapter on the Most Sacred Mystery of the Eucharist (§57); and indeed a new rite for concelebration was required (§58 out of 58). But it became one of the first things the Consilium did. Why? I can only assume because it was what had already been decided on, before the Council, as a priority.
The unstoppable momentum is illustrated in a footnote. Members of the Consilium having developed the first iteration of the Nous Ordo, tried it out in October 1965, including a replacement for the Canon. The Holy Father heard of this and was clearly dismayed. It is apparent that he did not know what they were up to:
'His Holiness wishes to know what kind of revision is being undertaken - minor changes or substantial reforms...?'
'In view of the exceptional importance of the Holy Mass, which is a sacred and age-old patrimony of the Church, His Holiness wishes the Consilium to exercise great caution both in organising experiments in this area and above all, in proposing innovations.'
'I hasten to tell you of His Holiness' desire that the Canon itself be not altered, at least for the time being.'But the genie was out of the bottle, and Paul Vl could not put it back in. The great caution he advocated was anathema to the Consilium: Bugnini boasted that it was because he was bold that the Consilium was successful. The Canon had already been rewritten; the Mass had already been re-written. The experts were annoyed at the Holy Father's intervention - but it only delayed their project: it did not alter it one bit.