If you haven't seen Jim Klar attack anybody with a tanto during a yudansha test, ask him to attack you. Very powerful and honest. Be ready to move off the line quickly!
I haven't seen Jim sensei attack during a yudansha test; I'll ask him to attack someone else so I can watch closely.
Thanks for your explanation of what the assumptions might be in the test video; they seem reasonable, and would explain why uke is leaving that second arm dead. I still am a bit surprised at the openings, though... shouldn't crisp, medium speed good technique still have you positioned such that those aren't there? I'm wondering whether it's an issue of nage's position, or of nage not really taking uke's center and "deposturing" uke so the opening wasn't viable... or something else.