User blog comment:FairyRaven/Fairy Tail Chapter 357: The Nine Demon Gates, Review and Commentary/@comment-112.198.64.42-20131027154249/@comment-7418318-20131027173730

It was said that the royal family took stuff from the book of Zeref and combined it with Celestial Spirit Magic.

If the information in the book would have already incorporated Celestial Spirit Magic, why would they have told it like that?

Thus I believe that the book of Zeref did not contain any mention of Celestial Spirit Magic.

That's not to say that Zeref didn't have any contact with Celestial Spirits. Considering his 400 years of life and how Celestial Spirit Mages were more numberous in the past there were surely plenty of opportunities for such a meeting.

But the existance of the Eclipse Project is hardly a proof for that.