It's odd how different rules seem to apply to different pieces of evidence.
Most of the time we agree DNA carries no date, yet somehow AK's DNA on a kitchen knife makes HER the one who stabbed MK!
Frankly, I'm amazed that anybody takes any of the testing on that knife seriously, but pretending for the moment that Stefanoni's results mean anything, AK is known to have cooked and eaten at RS' apartment, so we should EXPECT to find her DNA on some of the utensils there. A few molecules of AK's DNA on the handle does NOT mean she touched the knife on the night of the murder.
MK's DNA on the shaft of the knife is slightly more significant, but of course there's nothing approaching the quantity we should find if MK had been stabbed with that implement. And as it turns out, it isn't at all clear that ANY of the DNA is a match to MK.