When is a sequel not a sequel?

One of my all-time favorite films, The Last Detail, was adapted from a novel of the same name written by Daryl Ponsican, who wrote a sequel featuring the same three main characters called Last Flag Flying.

Quaid, Nicholson and Young
 in "The Last Detail"

Now, one of my favorite directors, Austin’s own Richard Linklater, is completing work on a film adaptation of Last Flag Flying, the script of which he co-wrote with Ponsican. However, both Ponsican and Linklater insist the film, unlike the book, is not a sequel even though the story line of the movie essentially follows the story line of the book.

In Hal Ashby’s original film, the three main characters (and the actors who played them) were Badass Buddusky (Jack Nicholson), Richard Mulhall (Otis Young) and Larry Meadows (Randy Quaid). These are the names of the same three main characters in the novel Last Flag Flying. For the film version, however, their names have been changed to Sal Nealon (Bryan Cranston), Mueller (who doesn’t have a first name and is played by Laurence Fishburne) and Larry "Doc" Shepherd (Steve Carell).

Fishburne, Cranston and Carell
in "Last Flag Flying"

Ponsican is publicly proclaiming that while his novel Last Flag Flying was a sequel to The Last Detail, the movie version of Last Flag Flying is definitely not a sequel to The Last Detail and will not be promoted as a sequel even though, except for the name changes and a few other details (no mention is ever made in the new film of the shared event depicted in the original film that bound the three together), the film is a faithful adaptation of the novel.

New editions of both books have recently been published and they contain prefaces from Ponsican on the origins of both the books and the movies adapted from them.