Interestingly, on Gaiman and attribution, he came out with a graphic novel, The Books of Magic, with a main character very similar to Harry Potter. This was 7 years prior to Rowlings publishing the first book. His response to that similarity was equally charitable, chalking it to creators tapping into the same unconscious material.

Before either you had Luke Kirby in 2000AD. While it’s debatable whether Rowling would have been reading Vertigo comic books, Gaiman wrote for 2000AD.