follow the way how duplicated npc are named.
// the number behind the NPC name must be above 1000 ( if you had not changed another )
// you can have 127 npcs.
prontera,151,171,4 duplicate(mission_board) Prontera Mission::1001 837
prontera,155,171,4 duplicate(mission_board) Byalan Mission::1002 837
prontera,159,171,4 duplicate(mission_board) Payon Cave Mission::1003 837
1001 ~ 1127