When playing on a drunk world, defeating one of the two world evil bosses (in my case, BoC) reports the other (EoW) as also beaten despite having not done so.
The game tracks them as a single boss, NPC.downedBoss2, because the game doesn't expect you to fight both. If you'd like to fight both, you'll just have to remember not to skip the alternate boss.
When playing on a drunk world, defeating one of the two world evil bosses (in my case, BoC) reports the other (EoW) as also beaten despite having not done so.