User blog comment:Omega natsu2/Chapter 397: Steel, Predictions./@comment-77.195.192.186-20140824124059/@comment-4999650-20140824130630

Hm I don't think we are receiving 3 chapters at once, because it would've been announced someplace else. I think Mashima is simply saying that he has to submit 3 chapters for the next 3 issues on a specific date.