User blog comment:IamJakuhoRaikoben/Chapter 373: Life or Death?, Review./@comment-68.8.113.239-20140301014438/@comment-7418318-20140301015834

The Eclipse Gate was only finished shortly before the X791 GMG and needed several GMGs to siphon enough magic power to work.

I very much doubt that in X777 they had even started construction yet (or planing for that matter) and there's no way it could have already held the necessary magic power.

If there was any sending through Eclipse Gates going on it must have been through another, not yet known gate. Most likely from the other end (i.e. pushing from 400 years ago, rather than pulling from a more recent time).

And why would it bother Igneel if E.N.D. was another Natsu. He'd know it wasn't his Natsu, so he wouldn't be stalled from killing him, not with what was at stake.