Just a few days ago, reports were saying that both SM Entertainment girl groups f(x)and Red Velvet would have comebacks in the fall after Girls' Generation wraps up their promotions. Now another report is giving a more specific comeback time period for both groups.

Sports Donga reported that f(x) would have their comeback as a 4-member group towards the end of this September. When f(x) performed at the '2015 London Korean Festival' the girls had also said they would have a comeback this fall and SM had also mentioned this as well when they announced Sulli's departure from the group, so it seems like September may be the month!

Red Velvet are reported to have comeback either right before or right after f(x). Reports say they'll release a new album in the beginning of September, or if their preparations are delayed, then at the beginning of October at the latest.
 

If this is true, it means all three of the active girl groups in SM Entertainment will be promoting in a row, or possibly even overlapping in promotions this fall.