I think if there's going to BE a masterpiece, it's the first one because it's fresh and new. And there's a difference between good reading material and a masterpiece.John Grisham couldn't get anyone to print his first book "A Time To Kill," so he had it printed himself. After that, it was all uphill. Many people who have read Grisham's, including I, consider it to be his masterpiece.
And some, like Margaret Mitchell, only had one book in them. Who's to know if her other writings would have been simply anti-climactic?