ANGERME's very, very early single announcement made me think...
Groups with summer releases that might release their next single around the date of ANGERME's:
- Morning Musume
- Beyooooonds
- Juice=Juice
Groups with spring releases that should get a release before:
- Tsubaki Factory
- Kobushi Factory
Though to be fair, Kobushi's calendar is packed (album, stage play) so they might push their next single to the winter months. Which leaves us with Tsubaki.
Personally I think there are two reasons why they're waiting so long to announce the next Tsubaki single: Kiki's injury and to not take steam off Beyooooonds. They probably thought Kiki would be better by now so they could announce the new single now - and I wouldn't be surprised if Nineteen no Shinkirou was supposed to be on the new single. They might work on a new single without Kiki right now.
I think the following release plan might be possible, judging by how they usually left a week or two between releases this year:
October:
Tsubaki
November:
ANGERME (announced)
Morning Musume (need to promote those new members)
December:
Beyooooonds (they need another single this year or else they'll lose momentum)
Juice=Juice (but they might do a digital release instead considering they already had two physical releases this year)
Kobushi (will be busy with their stage play until November 24; if any. Juice=Juice also had a year of only one single when they released their first album.)
The last singles were either announced a month before release (Jinsey Blues being the fastest between May 12 and June 12; Accha Accha and Oh No Ounou being announced one month and a few days in advance). Usually only releases linked to important dates (graduations, debuts) were announced longer in advance (Bitansan 2 1/2 months, "Hitori de Ikiraresou"... a bit more than 2 months, Megane no Otoko no Ko a bit more than 3 months; only Sankaime no Date Shinwa didn't have an important announcement linked to its 2 months in advance announcement). I left out the newest ANGERME single because... outliers and such lol.
I fear we should really consider Juice and Kobushi not getting another physical single release this year. Which would suck especially considering they need to promote Yume and Riai, but then again Ruru and Nanami also debuted with a digital single.