User blog comment:FairyRaven/Fairy Tail Chapters 338, 339, 340: Review and Commentary/@comment-86.66.207.63-20130706094810/@comment-7418318-20130707091342

That still leaves the possibility that something special will happen if the 12 are all contracted to the same mage.

Or maybe that "something special" isn't something that happens automatically when the Zodiacs come together, but rather something that must be activated by the mage(s).