Stick shaker too late
safta's experiment shows a big hole in the cheese. If normal recovery won't work, then I submit the stick shaker is coming on too late. Mind you the software revisions to account for trim state bodes to be complex. More likely is a revision to stick shaker recovery procedure when the trim is way back. We also have the Buffalo crash to consider.
Up to a couple months ago, nobody would believe that a crew would just sit there while the A/P wound the trim back until the stick shaker came on.
As far as minding the store, usually PF minds the instruments and PM is dividing his time between looking outside and and crosschecking the instruments. But here we have a teaching situation. Possibly a critical portion of those 100 seconds while the speed was deteriorating were consumed by PM giving teaching such that all attention by the junior pilots was focused upon a PM who was not monitoring.