A couple of news articles from some news sources mentioned "rapid 3 month succession", but that was about it.
http://oops-music.com/info/view_news_rss.html?nid=56540
This is the one I recall seeing.
http://detail.chiebukuro.yahoo.co.jp...il/q1043075175
Seems as though Japanese fans were wondering too and they thought it would be 3 months in a row as well. But I guess September through December for the next two singles are open now.