Warning: spoilers ahead for Batman: Three Jokers #3!
Did DC Comics screw up their final twist in Batman found a means to have every question he could think of answered, the shocking revelation that there were three Jokers was made known. However, the context of this question from the past seems to directly conflict with the even more shocking reveal at the end of Three Jokers in the present...or does it?
Back in Johns and Fabok's "Darkseid War" from their run of Justice League in 2015, the Dark Knight found himself with access to the powerful Mobius Chair in Justice League #42 that belonged to Batman confided in Green Lantern, sharing the Chair's reveal that there are three Jokers.
In Batman: Three Jokers, the Dark Knight finally investigates the notion of three Jokers operating in Gotham, which leads to an intense confrontation between the Clown Princes of Crime and Red Hood, Batgirl, and Batman himself. The Jokers work together about as well as you'd expect, with only one left by the story's end - the Comedian, whose true intent was to heal Batman of the trauma surrounding Joe Chill so he could become Bruce Wayne's greatest source of pain. However, another reveal comes at the end of the story, where Bruce reveals to Alfred that he's known Joker's true name since the first week they met. This reveal has been met with some confusion and criticism from fans due to the events surrounding the Mobius Chair in Justice League. If this is true, why did Batman waste the boundless knowledge of the Mobius Chair on a detail he'd already worked out?
But there's a simple answer: Batman was still testing this alien technology. Batman wasn't asking the chair for Joker's name because he didn't know it; he asked for the same reason he asked the chair about his parents' killer, simply testing more obscure information. Of course, Batman didn't actually know as much as he thought, and so he was shocked and derailed by the answer, but had the chair confirmed what Bruce believed he knew, he would likely have continued on to more and more complex questions.
In the end, DC's final twist of Batman: Three Jokers didn't actually create a plot hole, but the degree of subtlety seen in Justice League #42 does initially suggest what at first appears to be a continuity error. Seeing as how the issue was published literally years ago and it has most likely been awhile since many have read it, it probably would have been helpful for readers to have been reminded of the specific Justice League scene in a or two of Batman: Three Jokers itself - in the world of the story, Johns' forward planning can't be criticized, but there are plenty of readers who would be happier if that was true in the real world as well.
