This makes me think of the mechanics of modern day knife attacks vs battlefield weapon attacks. I'd say these weapons defenses then (at least knife defenses) are from an era that has passed by. To know your attacker has a knife is probably an exception and not a rule to knife attacks.
You know, I'd have to agree with this at least in principle. I know of "exceptions", but I also know that some of the scariest incidents I've been involved with involved attackers who were theoretically unarmed. Because the environment we were in had safeguards against them being armed. But it occured to me that those very safeguards pretty much meant that if they had a knife I wouldn't know about it until it was too late.
Most of these people I trusted. But there were exceptions.
Then, a couple of years later a gun materialized on the person of one of these "unarmed" people. It had gotten past the safeguards.
I keep trying to convince myself that the knife I see doesn't scare me, the one I don't see does. Truth is, they both scare me.