Ah, but you’re presuming that the rudder trim was physically at FSD and the indication system said so as each of the aircraft lined up.
I have yet to be convinced that there is no possibility of a latent defect in the rudder trim system in these aircraft. In each case there has yet to be any first-hand evidence-based explanation as to how and when the rudder trim came to be at FSD before take-off. I have spent many thousands of hours over many years tracking down weird faults in complex flying machinery, which faults were almost invariably easily dismissed as pilot error but turned out not to be.