Except the thing that leads me more to cock-up than conspiracy is normally they don't withdraw anyone from anything KSS related because of auditions or additions to groups etc. After all Kobushi and Tsubaki are still there even now.
Good point Could it just be a case of whoever typed out the list forgot which of the girls would be absent around that time or just decided to list all of the Tsubaki members without thinking that several of them would be away taking part in the Momusu stage musical?