To clarify for the benefit of Sirpeterhardingslovechild in post #177, if the handle is displaced from its housing with the seat pan pin out, the pin will not go back in the correct hole. End of.
Assuming the handle was only 'soft pulled' to the first detent and hadn't fired, which has happened several times between three types I've flown in my career, it can be re-seated, not without losing a few heartbeats, and the pin reseated correctly. Drama over. Rare but documented.
However, this small displacement opens a gap between the handle base and its housing which the pin can be (and has been) pushed into. In this case, the handle is still at the first detent, cannot be reseated and is liable to fire the seat with a further upward pull of sufficient force.
If the seat occupant was to relocate the pin, by feel into the gap they would be none the wiser. The error could only be seen by adjusting the QRF/paunch/fat thighs and looking vertically down to check the pin was centrally located in the handle. I always checked by sight before unstrapping, particularly after seeing pictures, pre-dating the incident in question.
Anyone looking in or down, checking that the pin is fitted, particularly with parallax from peering into the cockpit, could see the pin's handle and assume that it was safe if they didn't look to see that the handle was housed and the pin CENTRALLY LOCATED AND FULLY HOME.
I hope this clarifies for those who have a little bit of (dangerous) knowledge. I find the level of amateur speculation here appalling. This incident was close to me on several fronts.
Ray.