^
Ok, I'll try to explain how this song works.
The senbatsu members are less than in the previous single (11 if I'm not wrong), that means 11 girls are featured, they will be always in the front row and will probably go to TV shows. They are "the visible face" of the single. It's as BINGO or Sakura 2008. Lots of girls were there, but just a few got close ups, solo shots, solo lines and so on. That is senbatsu in THIS case.
The non-senbatsu members will be at back, will probably get random shots in the PV and won't really be song flagships.
If you see the AKBINGO video, the senbatsu girls have different clothes and the camera focus on them. The other ones are... chopped liver.