You realize, of course, that this includes only a small portion of the Smiths whose entries can be found in Allen J. Hubin’s Crime Fiction IV. These came from Part 9 of the online Addenda to the Revised CFIV.

   The first of these is, so far as I can tell without having actually having read one, a prime candidate for inclusion in Kevin Burton Smith’s online compendium of fictional private eyes, to be found at thrillingdetective.com:

SMITH, CYNTHIA (S.). 1934- . Add confirmed year of birth & middle initial; delete previous reference to CA. Author of books on marriage and business, plus a five book series of adventures of Emma Rhodes, “private resolver” who traveled around the world solving problems of the rich and famous for a $20,000 fee. Results were guaranteed within two weeks or the fee was returned.
      Impolite Society. Berkley, pb, 1997. Setting: Portugal.

      Misleading Ladies. Berkley, pb, 1997. Setting: England.
      Noblesse Oblige. Berkley, pb, 1997. Setting: Brussels.
      Royals and Rogues. Berkley, pb, 1998. Setting: Russia.

      Silver and Guilt. Berkley, pb, 1998. Setting: London.

SMITH, MARY-ANN TIRONE. 1944- . Ref: CA. Born in Hartford CT; married Jere Smith. Author of several novels, including one literary thriller included in the (Revised) Crime Fiction IV. See below.
      An American Killing. Headline, UK, hc, 1998. Henry Holt, US, hc, 1998. Setting: Washington DC, Rhode Island. [True-crime writer Denise Burke’s research into a new book may be involved with the death of a US Congressman.] Note: FBI agent Penelope “Poppy” Rice, a minor character in this book, reappeared as the primary detective in Love Her Madly (Holt, 2002) and at least one other subsequent book.

SMITH, MICHAEL MARSHALL. 1965- . Ref: CA. Author of science fiction and thriller novels and short stories. Lives in London; his first three novels are included in the (Revised) Crime Fiction IV.
      One of Us. Collins, UK, hc, 1998. Bantam, US, hc, 1998. Setting: Los Angeles, 2017. Publishers Weekly: “Smith’s ear for the nuances of classic hard-boiled narrative is surpassed only by his skill at exceeding expectations for the conventional mystery/suspense tale.”
      Only Forward. Collins, UK, pb, 1994. Bantam, US, pb, 2000. “Futuristic work that features Stark, a tough loner who is hired to find and retrieve a kidnapping victim in his home metropolis.”

      Spares. Collins, UK, hc, 1996. Bantam, US, hc, 1997. Setting: Virginia, future. [A former cop named Jack Randall frees several clones being held prisoner for their body parts.]

SMITH, NAOMI GLADISH. 1935- . Add confirmed year of birth. Born in England to American parents, now lives in Illinois and Florida. Currently the author of Christian fiction; her first book was a gothic romance, a mystery novel included in the (Revised) Crime Fiction IV. See below.
      Buried Remembrance. Ace, pb, 1976. “She fled the pain-filled memories of love, but Death would not let her forget …”

SMITH, NEVILLE (ROY?). 1940-1998? Add tentative middle name and year of death. British actor and TV screenwriter with one film to his credit; also the author of the novelized version. See below.
      Gumshoe. Fontana, UK, pb, 1971. Ballantine, US, pb, 1972. Setting: Liverpool. Novelization of film: Columbia, 1971 (scw: Neville Smith; dir: Stephen Frears). Leading character: amateur PI Eddie Ginley (Albert Finney). A Time magazine review of the film is available online.

SMITH, WYNNE. 1953- . Add year of birth. Author of a regency romance novel sufficiently criminous to be included in the (Revised) Crime Fiction IV. See below.
      The Rushmoreland Rubies. Pageant, pb, 1988. Setting: England, 1800s. Published as Regency Romantic Intrigue Series, Book 1. [Lady seeking the rubies disguises herself as a housemaid in the home of the man who inherited them after the mysterious deaths of two heirs.]