Given your latest post, it looks like we don't have much of a disagreement at all. I was thinking along the lines of knife encounter = encounter + knife somehow involved, rather than focusing on assassination type attacks.
Regarding assassination type knife attacks, do you have any actual statistics? I respect Mr. MacYoung, so I don't want to dismiss his claim, but I don't ever seem to hear anything about such attacks on the street. (Prisons are a different story.) If you have any statistics or statistical sources, I would like to know about them.