Bingo! It was, as a result of their vagueness, that certain bihops and priests were able to introduce 'novelties' into the liturgy. This was not unique to the US but, as we have already seen, worldwide.
To cite an example, when I wrote the local diocese about my (then) pastor attempting to introduce liturgical dance into the liturgy, the Director for Divine Worship responded in favor of the pastor and quoted from a VCII document on 'multicularism'. After choking with laughter, I wrote her back citing Sacrosanctum Concilium and Canon law which states that catholics have a right to a valid liturgy. I won; they lost.
The victims of these shenanigans were pew catholics who never bothered to actually read the documents. They simply went along on the assumption the bishop would not delude them. For many years, I was one of them. Then I discovered this forum :-)
That's very true. I often wondered how many bishops themselves had read the documents, though, or if they were simply relying on somebody else's creative interpretation of them. And then inevitably the interpretation took on a life of its own and nobody even thought of questioning it...
The liturgical innovations are but a part of the controversy. The bigger point for SSPX, especially now that the Traditional Mass is defended by Rome itself, is the Vatican II ecclesiology that they view as too ecumenical and problematic.