Well, you might start with 110.14(A), which prohibits damaging the conductors at a terminal connection. You 've got to keep in mind that the code provides necessary provisions (90.1)for "practical safeguarding of persons and property from hazards arising from the use of electricity."
My point here is that the wire nicks have to be bad enough to really count! Consider how much damage occurs when someone wire-brushes an aluminum conductor prior to putting on oxide inhibitor compound--I don't recall any installation instruction saying that I have to wire-brush lengthwise with the conductor. If I brush across the conductor, chances are pretty good that I will nick strands of that conductor. But, there might be some general statement in the installation instructions for the listed termination device to the effect that you can't nick or damage the wires while preparing them for termination. Just to add further complexity to a simple query, there might be a technical distinction between nicking a wire, and scratching it. A nick will leave a sharp cut across the strand that will fracture readily, while a scratch would possibly leave a smoother notch across the strand -- increasing resistance -- yet not necessarily creating a fracture zone as readily as a nick would.