Yes they did air all of them back to back to back.
Yes it was torturous.
Yes some silly dudes have tried to retroactively paint it as "brilliant" and not one of the worst decisions ever made in the production of a television show.
Well, in retrospect you can kind of see why they did it. Clearly Kadokawa/KyoAni had plans to make a movie of
Disappearance first, and then there was a conversation like this:
Executive A: Guys, we have a problem. The plot of Disappearance specifically references an earlier short story that we didn't cover in our original adaptation. We have to cover that somehow before releasing the movie.
Executive B: So make another series of the anime, I guess? Haven't the fans been asking for that forever? What's the issue?
Executive A: We don't have enough material to fill a whole new cour! There are only, like, three stories we haven't covered that take place before Disappearance, and none of them have enough impact to carry a season!
Executive B: Well, we did that weird non-chronological airing thing last time, right? Let's keep thinking out of the box. If the new stories aren't awesome enough on their own, maybe we could just slot the new stuff into the old season. Call it an upgrade.
Executive A: I
suppose that could work. We could surprise the fans by pretending it's just a rerun and then BOOM! New stuff. Yeah! We'd be the talk of the internet!
Executive B: Then let's go with that!
Executive A: There's still a problem, though. Even if we slot them into the old season, we're still gonna have to fill a whole second cour with these new episodes. Those three stories are never going to fill a whole cour - two of them are tiny one-chapter deals, and even the big one is five episodes at most.
Executive C: Oh, just shove in a few recap episodes, what's so hard about that?
Executive A: If you make a suggestion like that again, I'm sending you back to Shaft. We
don't do recaps.
Executive B: Seriously, dude. That was low. Still, we do have to pad the material out somehow. How about expanding on one of the stories?
Executive A: Go on...
Executive B: Well
If I'm remembering correctly, one of the stories revolves around a time loop. You only get to see the final loop in the novel, but if we showed some of the others
Executive A: What's that story called again?
Executive B: Endless Eight.
Executive A:
Endless
Eight
?
Executive B:
Executive C:
Executive A: Gentlemen, we are about to enact the most glorious troll in all of anime history.