At least with Sam'l Clemens, you could point to an individual person and say, "There, see? He (or she) wrote that. He (or she) sat down and conceived the plot, fleshed out the characters, scrawled (or typed) it all out, letter by letter, sentence by sentence, and finally typed (or scrawled) 'The End' when finished.
I was devastated in later years to discover that most of the "series" books, for children or otherwise, were written either by a staff of writers or farmed out to ghost writers by the publishing companies --including the "Hardy Boys" series. (And the Nancy Drew mysteries, too, I found out.)
How hard my childhood icons fall.
.... And not just with my favorite books, either.
Terry, 230RN