does that make the over-tightening of the shackle bolt an aggravating factor to the same root causes?
No
Or is the over-tightening of the shackle bolt now the cause of the accident
No
unsafe condition of the handle and its pulling as contributory factors
Yes
And would the distinction have any significance for liability or culpability?
If a company were aware that over tightening of said shackle bolt in a zero zero ejection may result in the failure of their seat - in my opinion they are NOT culpable but they are liable.
Just my irrelevant views as I'm not a SME.