Nice and interesting this "stall-recovery-procedure", but...
I was told and teached how to recognise and avoid such an event. (and yes I did practice stall-recovery-procedures in many types)
Sorry, but 3 pairs of eyes could and should have seen/scanned/observed the (negative) speed-trend!
And as an instructor you know this kind of flights and (for me) you are more "on-the-ball".....just my few cents