With all this awareness, why did this SI not highlight the lack of action to deal with this problem, and why could the shackle bolt have been so inappropriately over tightened after so many years of this seat being in service?
It could NOT be overtightened when fitted in the seat bay because it (the drogue shackle) was pre-assembled (bolt already fitted) before sliding into an open scissor shackle and the BTRU cocked. If it was too tight it would simply of not have gone into the scissor shackle. It was the advent of extending seat servicing times in recent years which meant they had to frig a way of undoing the drogue shackle bolt to enable the beam crack testing to be carried out. Simply the shackle system was never really designed to have the bolt removed/fitted in-situ.