I haven't read all the posts so I don't know if this has been addressed yet, apologies if it has.
One of my other characters just failed his assassination on someone, but the death came from blood loss before the target could get in their next attack.
Seems like since the death wasn't from a direct attack by that person it didn't register with the system. Don't know if there's any way to track "last strike" for purposes of this, but if so, that might be a good addition.
Ogdaro