This portion of your statement . . .
with the modern ability to imprison indefinitely serving as a supportive element.
No, it suggests that one part of the Pope’s argument is provisional, not the whole of it. If I say that “rape is inadmissible because it is a violation of human dignity, and it will land you in prison”, this is not a provisional teaching based on the current penal code. The current penal code is brought up, certainly, but the argument doesn’t rest on this provisional element alone.
Human dignity is unchanging, though our understanding of it might develop. The provisional element in these writings, insofar as human dignity is concerned, is that the Church’s understanding of human dignity was once more ignorant than it is now. This is explicitly stated in the CDF document when it says, “
This development centers principally on the clearer awareness of the Church for the respect due to every human life.” This is the foundation of the teaching, that the Church has a clearer understanding of human dignity now than it once did.
And was there not a violation of human dignity last week before this teaching?
According to the Pope and the CDF, in their own explicit words, the Church has a clearer understanding this week than it did last week, so what was permitted before (in ignorance, presumably) can no longer be allowed. That is what the text literally says, regardless of whether or not such a teaching is correct or prudent.