it inexorably follows that the previous hole was the trim being set to full deflection before the flight. Be good to know who and why.
That certainly is a puzzling question. Someone screwed that rudder trim full scale left either before the take off or during the take off roll. We will never know who that "someone" was. Readers may recall the circumstances of the crash of the Helios Airways 737
See:
https://en.wikipedia.org/wiki/Helios_Airways_Flight_522. The crew took off unpressurised because neither pilot noticed during their preflight the pressurisation selector was set to Manual and not Auto then further failed to compete the after take off checklist properly so missing the lack of pressurisation for the second time (complacency by the captain for not monitoring the actions by the F/O).
The pressurisation controller had previously been set to Manual during a trouble check by servicing personnel. They omitted to set it back to Auto afterwards. Of course it should have been picked up during the crew preflight checks but both the captain and first officer were slack in their job and missed the fact the selector was still in Manual. But at least the culprit was known to be the maintenance staff. Nothing has come to light in the King Air accident who set the rudder trim full scale left. Not that it affect the final outcome though.