Thread:Tupka217/@comment-26127492-20190627035407/@comment-26127492-20190627063658

Those are very specific events, though, and they don't line up with any other continuity. It's also the same creative team, and both stories are set outside of the main DCU. Lee Bermajo also said this of the series:

"Damned is a quasi-sequel to Joker in that you don't necessarily have to read Joker to read and enjoy this book but if you've read Joker, I think people will find they're brother and sister books." (And we now seen to know why)

It even shows the corpse of Johnny Frost, a character created specifically for that story, who was bleeding out as the Joker and Batman on a bridge fought at the end of Joker. I think that's a pretty big indicator that it's the same narrative.