For those who have forgotten because of revisionist history, it was Jerry Robinson who initially created the Batman's greatest foe, the Joker, and it was Bill Finger who wrote the first story featuring the character.
Now, Bob Kane did work on the Joker character, and his contribution to the mythos should not be marginalized in this instance. He did create Batman after all (though it was obviously inspired by the villainous character in the 1926 movie The Bat). Still, it is not entirely correct to give Kane full credit for everything in the early Bat-verse. It also is not right to take away a contribution from him, either. During the process when Kane was fleshing out the character, Bill Finger produced a photo of actor Conrad Veidt as he appeared in The Man Who Laughs from 1928. It was apparently typical of Finger of to do extensive research like that for a project. Viedt was the perfect model for the Joker, everyone agreed, and it is pretty much how the character appeared in Batman #1.
The production of the Batman titles did not happen in a vacuum and maybe the ultimate product should be considered at least in part as an ensemble effort.
As far as creator rights go today, DC has to be cautious in bestowing credit because of royalties and ownership issues. Well, from a business standpoint contracts were signed, people got paid for the work, that's howo it stands. I am not saying that was right, but it is how the biz worked back then (and today, I understand).
My observation is that if The Bat and The Man Who Laughs came out in the 80's and someone tried to pitch comic characters based on them today, it would be considered a straight rip-off. Kind of like how Deadpool is just Deathstroke composited with a homicidal Spider-Man, as designed by He-That-Shall-Not-Be-Named (when Deadpool first appeared I just assumed he was a Spider-Man clone). What made Batman and Joker unique and not just a copy is the early departure into originality from the source material.
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