Are you feeling some problem during turning ?

My thought is that the slot in the pulley was cut with a tiny saw, and hence has a radius, and bends the pin when the nut is tightened. Over time with careful attention to the torque when tightening the nut, the pin will bend until it conforms to the radius on the slot. The very first time it's tightened by a new owner with gusto, it will be forever bent to fit. Further, it will be misaligned with the large pulley on the spindle. At least a little, at first, and then finally, more. In any case, in my 50 years with the DB, not enough to bother. Idler can be aligned by adjusting the clamp bolt. You can always straighten or replace the pin if this bothers you.