This is one thing that's hard for people living under modern licensing to grasp. Folks just adapted books and didn't really bother with rights in this era. The most popular play in America second half of the century, for instance, was ALL THE DIFFERENT adaptations of Uncle Tom's Cabin.
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The novel disappeared from the 1850s to the 1870s. It was kept alive by the stage, and none of that money was going to either Shelley or Bentley. No such thing as subsidiary rights at the time.
By the 1880s, it was definitely out of copyright, and reprints began.
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