And these are only the direct adaptations. Disney's very first work, "Alice's Wonderland" (not the movie, just a dreamlike short), was a riff on Carroll's work. It was published less than 30 years from Carroll's death and about 50 years from publication.

It's interesting to think about the term "existing cultural icons". On first glance it seems like the term weekens the issue because it makes it sound like these are folk tale like things that somehow magically manifested. What happened though is that someone actually invented a story, it got retold over and over and evolved into what we have now. This would have been prevented by modern copyright. The original author wouldn't have allowed others to reproduce their work. The work wouldn't have evolved and probably even been forgotten.