In the comics they had announced that there wasn’t just 1 Joker, but rather that there were 3. Jack Napier was only one of the 3. Also, to true comic book form, the Joker never really stays dead. It could be a simple slip up in writing but I doubt they (producers directors and even prop designers) would have made such a huge mistake, let alone focus on it in such a way.

In the comics they had announced that there wasn’t just one Joker, but rather that there were three. Jack Napier was only one of the three. Also, to true comic book form, the Joker never really stays dead. It could be a simple slip up in writing but I doubt they (producers directors and even prop designers) would have made such a huge mistake, let alone focus on it in such a way.