Why important? Because they referred to council fathers’ reasoning behind liturgical changes, positioning them in the history of such change, from Pius X to Pius XII.
[T]he idea that the council was a continuation of work already begun was obscured by numerous commentaries that treated [Sacrosanctum
Concilium, the document in question] as a departure from the past, the beginning of a “new” liturgy for the “new” post-Vatican II church.
This brave new world concept, was declaimed happily by Joseph Gelineau, S.J., in his book The Liturgy: Today and Tomorrow (New York: Paulist Press, 1978): “the Roman rite as we knew it exists no more. It has gone. Some walls of the structure have fallen, others have been altered; we can look at it as a ruin or as the partial foundation of a new building… The liturgy is a permanent workshop.”
Indeed, you would think so, were it not for the missing references, wrote Benofy:
Readers of SC who are not familiar with the liturgical teachings of earlier twentieth-century popes and are not led by footnotes to the documents that explain them will almost certainly see SC as a document with no connection to the recent past. They are thus unable to see SC as the Council Fathers did – as the continuation of reform begun by Saint Pius X.
Not as a license to make it a living document, as many in the U.S. would like to consider the constitution.
“Had even some of these references to documents such as Tra le sollecitudini and Mediator Dei been kept in,” she continued,
it would certainly have been harder to interpret SC with a hermeneutic [interpretation] of rupture and discontinuity.
As it stands, Vatican II’s Liturgy Commission – inadvertently or by design – made it a lot easier for various people to interpret SC as advocating a kind of ‘year zero’ liturgical reform, disconnected from the reforms of the earlier 20th century popes. (Italics mine)
More to come on these behind-scene maneuvers, if that’s what they were, rather than well-meant omissions . . .