The knives were not dusted at the crime scene so that would not make any difference. They were dusted at the crime lab. And for that matter no one dusts the sharp end of a knife. You dust the blunt side and the handle. Jo?Kezzy is just making up evidence in her own head. They proved the fibre on the knife did not come from the dusting brush. It wasn't just the fibre, there was also rubber dust from the rubber that surrounds the screen. Two separate pieces of evidence did not get transferred from a dusting brush. The crime tech also testified the screen was cut with a serrated knife. The knife that held the fibre was a serrated bread knife.
Those fibers from screen came from knife and I think it was cut by the killer but not darlie.