If you're running +ML and plinking (I do that, does anyone else?), then it's fairly important. Especially if you're running +50 ML, that's a difference of 5 defense, which might be difficult to come up with while plinking.
It's not really a huge deal anywhere. A whole lot of monster defenses on the wiki (which I assume mafia uses?) are also wrong anyway. However, being accurate as you can is always nice.
If it'd be horrifying to fix, don't worry about it too much. I would think that it's just a small fix somewhere.
Such as in net.sourceforge.kolmafia.request.FightRequest.getMonsterDefense()
changing this
Code:
return FightRequest.monsterData.getDefense() + FightRequest.levelModifier + KoLCharacter.getMonsterLevelAdjustment();
to this
Code:
return FightRequest.monsterData.getDefense() + FightRequest.levelModifier + Math.ceil(0.9*KoLCharacter.getMonsterLevelAdjustment());
Seems like it'd do the trick.
Also, looking at FightRequest.levelModifier: Disco Face Stab reduces ML by 9, not by 10.
Which is found in: private static final void payActionCost()
EDIT: while i'm on the subject, Shieldbutt decreases either Attack or Defense by 5, depending on the message. payActionCost seems to think that it just reduces both by 5, without looking at the message.