Kingston,
Bit of a misunderstanding
. You're right in saying that the type of knife can make a difference in the usage (i.e. a short blade is better for slashing, while a longer one is more suited for stabs/thrusts). My point was that it shouldn't matter because you should attack the knifer immediately. By that, I literally mean move towards him/her with the serious intent to harm them. This is desirable because:
1) Creates the proper offensive mindset that is crucial
2) Can "psyche out" the knifer--he holds all the cards, yet youy attack HIM
3) Prevents you from entering a defensive flow that almost invariably WILL kill you
4) Stops you from freezing with shock/fear
About the legal comment: in the USA, you would be signing some VERY heavy waivers before getting into any of that. People can and will sue for ANYTHING, and a judge would convict you so fast your head would spin. I'm a little passionate about knife defense in particular because I have seen too many times what a blade can do to a person.
Hope I made myself more clear,
Ryan