I'm not sure as I haven't read it specifically. It might be about a man who is distinctively recognized by not wearing a hat, and perhaps his adventures, relationships or some kind of personal journey could be central to the story.
I don't know who the author of 'the man with no hat novel' is. There are so many novels out there and without more information, it's difficult to determine the author.
I'm not sure specifically which 'the man with many hat story' you are referring to. There could be various stories with such a title. Maybe it's about a man who has different roles or identities represented by the many hats he wears, like he could be a farmer during the day (with a straw hat) and a musician at night (with a fedora).
The moral could be about the importance of memories and the connection to the past. The old man's hat might represent his life experiences and the things he holds dear.
The man who mistook his wife for a hat is a story that delves into the mysteries of the brain and how it can play tricks on perception. It's a fascinating and somewhat disturbing account.