Isn’t most fiction writing like this though? You just don’t get to see it because it’s not so interesting and you don’t generally have a person (tolkiens son)

Isn’t most fiction writing like this though? You just don’t get to see it because it’s not so interesting and you don’t generally have a person (tolkiens son) making editing leftovers their life’s work. People edit, make major changes, names change, a minor detail in an early draft becomes a central plot point. Neil Gaiman definitely talks about development of his work like this. Tolkien seems to be particularly interested in having a body of his life’s work writing being consistent, but it’s not so out of line with how any fiction is written.