User blog comment:FairyRaven/Fairy Tail Chapters 338, 339, 340: Review and Commentary/@comment-86.66.207.63-20130706094810/@comment-7418318-20130707111700

Because people like to speculate about ever possibility, no matter how unlikely it is. And while it is possible that "The Gate to change the world" was indeed the Eclipse Gate, there is no definate proof.

But I don't think it is. The Eclipse Gate was created by combining information from the Book of Zeref with Celestial Spirit Magic. To me that sounds like the Royal Family (or more likely mages that they are allied with of employ) came up with the idea by themselfs, rather than finding it in some old book. Since Yukino called "The Gateway that changes the world" and Old Legend, that would mean this legend existed before the Eclipse Gate was invented.

So unless the legend came to be from knowledge that the seven Dragons carried back into the past with them (though I don't see how they would have learned that the Zodiacs were used to open the gate) or from some kind of prophecy, it has to refer to something else.