I think all the scars that you've mentioned do appear on the sword of the enemies whom I have encountered, and that means all of them are to be defeated by their own sword.
14 seconds sound clip from the Ninja Swords of Death movie soundboard.
You can hear this line at 01:17:15 in the DVD version of the movie.
Quote context
[...]
- You have no way to choose but to die if the sword has one. That scar is most harmful.
- It's a devil's wish. No one can prevent it. You must beware.
- And I think after I have killed Han San by using the sword, and it may turn bad.
- As to that 1,000, I will ask it from your dad.
- You can get it after the fight.
[...]