Thanks for confirming my post--note that the primary method in both the Papal writings AND the St A Missal is "interior."
Please don't mis-read my posts--the "make 'em sing" mentality is well-meant, but secondary to "interior participation."
And as for "make 'em sing," the FIRST vehicle mentioned is Gregorian Chant Ordinar(ies.) Not Fred Rogers tunes, which are ipso facto inappropriate for worship.
Excuse me, but your point was that
[active participation] "does not necessarily require activity, song, or verbal response."
I think I have documented at a minimum that both song and spoken response (at appropriate times) were strongly encouraged, as opposed to silent assistance. I hope you won't plead that, just because it fell short of an binding mandate, this strong encouragement did not constitute what was normative in the eyes of Rome. I feel quite comfortable with my position -- that more than a half century before Vatican II, Rome was gently but unambiguously prodding the laity to contribute more than silent assistance at Mass.