What does the history of fans of fiction and their nitpicking look like, especially before the mid 20th century?

by TokyoFoodie

I've always taken for granted that the modern concept of "fans" arose with the pulp science fiction fan groups of the mid-20th century, but as they say -- "there is nothing new under the sun."

Are there any earlier instances of this kind of fandom?

I'm especially interested in hearing about fans or groups that nitpicked canon in fiction. For example, did Sir Arthur Conan Doyle have to deal with letters arguing about canon in his books?

ibbity

Louisa May Alcott is believed to have received letters from fans complaining that she didn't marry off Jo to Laurie. She declared "I won't marry Jo to Laurie to please anyone!" and married Laurie off to Amy instead in the second part of the book (the first and second halves of the book were initially published separately.) That's the only specific example I can think of at the moment.