What is the correct term to describe literary works that are only partly fictional?

Solution 1:

The works you cite are wholly fictional. Being well-researched and more plausible than, say, a sci-fi yarn or Harry Potter doesn't change that.

If you were looking to invent a term, some that might apply include gritty (generally implies more realism than average, although that wouldn't apply to a well-researched comedy book), or even realistic.

Semi-fictional could describe a genre that in ad copy might say "Based on actual events" or "Ripped from the headlines" (at least per Wikipedia definition), but neither of the works cited seem to fit into that category.

Solution 2:

Fiction is fiction. Different eras and different audiences vary widely in the sort of background they demand, but every storyteller has to supply some measure of what W.S. Gilbert called "merely corroborative detail intended to provide artistic verisimilitude to an otherwise bald and unconvincing narrative." Verisimilitude may reside in familiar quotidian detail or romantic "history" or in the depiction of motive and mental states; but without some such detail there's no framework to set the story in and no identifiable connection with the reader's own experience.

Solution 3:

The Da Vinci Code is a secret history.

Secret history is ... used to describe a type or genre of fiction which portrays a substantially different motivation or backstory from established historical events.

John Grisham's books (at least the ones I've read) are not secret histories. Most fiction (unlike Harry Potter, LOTR) is set in the real world, and accurately depicting certain elements from the real world as background is very common in fiction. John Grisham's thrillers often go into details of the law and the legal profession more extensively than most fiction about lawyers, but this is just one point on a continuum, and I don't know of a special word for this.

Solution 4:

Semi-fiction and semi-fictional don't seem to be unusual terms. I would use them.

Semi-fiction is fiction implementing a great deal of non-fiction, for example: a fictional depiction "based on a true story", or a fictionalized account, or a reconstructed biography. Often, even when the author claims the story is true, there may be significant additions and subtractions from the true story to make it more suitable for storytelling. One such example would be Tim O'Brien's The Things They Carried. Wikipedia

from Google Books:

• While semi-fictional text can emerge in a directed way, we also highlight...
• Gathered here are some of Dreiser's best pieces of short fiction and semi-fiction.
• Metamorphosis: A Small Piece of Semi-fiction.
• The Retreat - A Semi-Fictional Memoir Exploring Common ...
• It is in any case a semi-fictional genre, novelistic in its own way.