Crab,
The excess torque could be for a number of reasons and it is only the effort required to remove the nut.
It is easily conceivable that the clamp up was correct.
At first glance in the picture in the report, the TR end of the control shaft there appears to be burnt grease that has migrated along the shaft.
It woudnt surprise me if it migrated to the nut end as well. As you can see it can get in to very small places as there are traces between the outer part of the inner race and the shaft.
The thread seems to be full of it as well. You dont need much friction in the thread to change the torque requirement in the nut. Ever used Loctite? It doesn't have much inherent strength but spread over the area of the thread?