The Halloween 2019 date is pretty blatant. That's definitely the one I'd go with. The Riddler was crazy to the point that I wouldn't trust anything I read in his journals, including dates.
Yeah, I guess prop dates should come second to dialogue. That 2001 Thomas Wayne campaign and 2000 document can be chalked up to bad props. I'd rather assume that than that Batman is dumb or the calender is different in this universe.
Also, Joker: Folie à Deux should be an interesting addition to the Joker timeline. It sounds like it will pick up after the ending of the last one, where he's in Arkham State Hospital, based on Harleen Quinzel.
My personal interpretation of the ending is that this is many years after the events of the film (14+ years, perhaps). Both Arthur and his psychiatrist are physically older. A young Bruce Wayne has become Batman and captured Arthur, sending him back to Arkham. Arthur realises that he created Batman when his parents were killed by clown rioters. Both he and his enemy are forever linked, Joker being born from the mistreatment from the rich while Batman was born from the rioting of the less fortunate.
He kills his psychiatrist after she asks him about his joke. I imagine that, in the new film, Harleen is his new psychiatrist. Perhaps he tells Harleen a different origin to the one we saw in the first film, keeping the multiple choice elements intact. The film might end up being essentially a musical adaptation of the classic Mad Love story then.
Also, there's no need to complain about the Joker's age in my opinion. Let's say Bruce Wayne starts his career as Batman at 25. Let's say he was 9 years old in Joker. That means he'd be Batman by 1997. Arthur Fleck was born in 1949 based on props, so he'd be 48 by this point. I mean, how is that much different than the age difference between the Batman and Joker of Earth-66 and Earth-89?
I know a lot of people are worried about it, but honestly I love the fact we're getting a Joker sequel. In the first film, we never saw the Joker. We saw a mentally ill man kill people who he felt deserved it. It's very much a beginning story, something the Joker would tell when recounting his origin, but it was not the Joker yet.
