Thanks, Br. Robert.  
The group selected by the Vatican to study the Church's teaching on contraception, was comprised of men and women [some married], clergy and hierarchy as well.  It was representative of the entire Church.  But Humanae vitae was written because of a fear of 1) violating the teaching papal infallibility which would have be demonstrated by 2)abrogating Pius XI's encyclical 'Casti connubii' [December 31,1930].  This encyclical, prohibiting contraception and abortion came on the heels of the July 1930, Lambeth Conference, [Resolution 15] which produced a relaxation of Anglican attitudes toward birth control.*

As you wrote, 'the bishops prohibit the sensus fidelium to enter into their deliberations and pronouncements"--which precluded the involvement or the whole church.
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Notare, Theresa, "A Revolution in Christian Morals': Lambeth 1930, Resolution #15: History and Reception" [Ph.D. diss., Catholic University of America, 2008]