Four-armed NPC's with Two-Weapon Fighting

[Bionikler]

I was wondering what the ruling is on all the NPCs with four arms and Two-Weapon Fighting is? The Multiweapon Fighting feat says that it "replaces Two-Weapon Fighting for creatures with more than two arms", so shouldn't these NPC's have Multiweapon Fighting? Was that rule ignored to balance the encounters, or was it simply an oversight when making the stat blocks?

Any links to official sources on this would be much appreciated.

[Nicolas Paradise]

Any specific encounters that you are looking at? The ones I can remember in book one namely the Kasatha Skeletons and Hetuath all have 4 attacks with the correct math so even if they have the wrong feat the math ir right.