The knives were taped so they couldn't be disarmed. Similar problems can arise if your attacker has a very thick jacket on or if he's got no shirt and is sweating. Sterile training often doesn't reflect the real, unpredictable world and all it's variables. Training should address when things go wrong and how to adjust to accomplish a goal. Defensive tactics and firearm training should cross.
Cross training is quite popular in sports and fitness circles currently.
The same idea should enter into officer survival. As in sports, it makes a more thoroughly trained person. Training gaps are filled this way. More about this later. Training should include dynamic confrontational situations with unorthodox attacks by instructors.