Good post Mr Mungus.
Yes I am quite surprised at the number of people who were/are dependent upon these seats just did not appear to know that much about them.
I have just reread my post that made reference to the original design. It went on to refer to the checks and balances that were in place commending the post that someone had made on another forum (AARSE) The hundreds of people in various formations who would have had an input to ensuring continued airworthiness. Some have disappeared altogether or watered down over the years. The design was just one slice of cheese.
I agree with others that there were two separate mechanisms (the seat pin and the shackle bolt) that came together leading to the tragedy. So far we [the public] don't know much about the pin. perhaps we might next week when the SI is made public. Reading between the lines it looks like MB/MoD have introduced a modification to address the deficiencies in both areas. They could have done one without the other. Could have done neither if they could have demonstrated ALARP.