How's that possible?
If you'd have a map like this:
NPC Code:
"level_a-1.nw", "level_b-1.nw"
"level_a-2.nw", "level_b-2.nw"
and you'd like to add level_c-1.nw in the north-east, you'd write:
NPC Code:
"level_a-1.nw", "level_b-1.nw", "level_c-1.nw"
"level_a-2.nw", "level_b-2.nw", ""
Can't see a problem...