A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 29 March 2015
desperate sacrifice - Political Battle: Destroy your target Courtier. Bow a target enemy Personality. Move him home. This movement will not be negated.
knife in the darkness - Ninja Battle: Move home your target Ninja Personality and a target enemy Personality; these movements will not be negated. Bow them.
iron armor - Card effects will not move this Personality. Melee and Ranged Attacks targeting this Personality have -2 strength.
so what will happen if desperate sacrifice/knife in the darkness is use on a target with iron armor?
Alex Jones (rules official), 30 March 2015
desperate sacrifice - Political Battle: Destroy your target Courtier. Bow a target enemy Personality. Move him home. This movement will not be negated.
knife in the darkness - Ninja Battle: Move home your target Ninja Personality and a target enemy Personality; these movements will not be negated. Bow them.
iron armor - Card effects will not move this Personality. Melee and Ranged Attacks targeting this Personality have -2 strength.
so what will happen if desperate sacrifice/knife in the darkness is use on a target with iron armor?
The "will not be negated" clauses negate Iron Armor's movement negation trait, so the Personality will move.
"Negate" and "will not" both indicate Prevention; unlike in Emperor Edition, no distinction is made between them.