For Big Bang, T.O.P's news of getting accepted into the military police for his mandatory military service has hurried the group's comeback. It has been reported previously that the recording of the new album is completed, and the group already shot their new MV. Because of the impending military service, Big Bang cannot delay the comeback any longer.
As for Sechskies, they were expected to make their comeback earlier this year, but it was postponed. They are reportedly already finished making their comeback MV. Sechskies is also scheduled to be on 'Weekly Idol' and have already filmed 'Running Man,' which shows that they have been ready for a comeback for a long time.
Although they might be competing somewhat with similar comeback timeframes, the two legendary idol groups will most likely have a mutual win-win situation; being from the same agency as well as being groups that have national popularity can only benefit both of them. These are meaningful comebacks -- this is perhaps Big Bang's last comeback before a potential long break for military service, and for Sechskies, they are breaking their long hiatus and re-entering the music scene.