User blog comment:B214/Volume 1 - 15 Discussion/@comment-1359322-20140120070807

This is nothing important just ignore this list.


 * Volume 1 - Asia
 * Volume 2 - Rias
 * Volume 3 - Yuuto
 * Volume 4 - Gasper
 * Volume 5 - Koneko + Sitri Team
 * Volume 6 - Asia
 * Volume 7 - Akeno
 * Volume 8 - Issei & Rias
 * Volume 9 - Issei
 * Volume 10 - Issei, Rias & Sairaorg
 * Volume 11 - Mid-class Promotion Test + Koneko
 * Volume 12 - Issei, Yuuto & Vali
 * Volume 13 - Millicas
 * Volume 14 - Ravel
 * Volume 15 - n/a
 * Volume 16 - Gasper
 * Volume 17 - Rossweisse
 * Volume 18 - Irina
 * Volume 19 - Xenovia

I guess it's possible for Akeno, Yuuto and Koneko to get another Volume.