Books have used the “XYZ: A Novel” format since the 17th century, when realistic fiction started getting popular. The term “novel” was a way to distinguish these more down-to-earth stories from the fanciful “romances” that came before, says Steven Moore, author of “The Novel: An Alternative History.” Then, as now, it was a tag that identified the kind of literature you were getting yourself into.
From Book covers still use the phrase “A Novel” for works of fiction – Vox
Not a novella?
Odd that the piece didn’t even mention one reason for adding “A Novel”: to distinguish short novels (40,001 words or longer) from long novellas (17,500-40,000 words). Steve Martin’s “Shopgirl” was properly labeled as “Shopgirl: A Novella.” [I’ve wondered whether some Spenser novels are actually long novellas…]