Yes, I see what you're saying.
But they're both measured in hit points (and even use the same scales), so anything that applies to the oddness of hit points similarly applies to nonlethal damage. Ergo, you can do nonlethal slashing and piercing damage with a knife, overcoming DR 5/Slashing.
Therefore, there's no mandate to describe it as being done with the pommel of the knife.
I'm afraid you've lost me. I'm not sure of the point you're trying to make or the direction you're taking the thread.