Signs of tanking starting showing after the war crimes storyline was abruptly ended.
Here's how 1984/85 season compared to the rest of the primetime soaps and the two rookie hits. I used the end of the war crimes storyline as the divider.
September 28, 1984: Requiem (season 4 premiere), rating 23.4 (season high), 2nd for the week. Finished ahead of The Cosby Show (September 27: Goodbye, Mr. Fish (episode 2), rating 22.5, 3rd), Dynasty (September 26: Disappearance (season 5 premiere), rating 22.2, 4th); and Murder, She Wrote (September 30: The Murder of Sherlock Holmes (series premiere), rating 18.9, 9th). Dallas (September 28: Killer at Large (season 8 premiere), rating 26.4) was #1. No Knots Landing on September 27.
October 5, 1984: Father's Day, rating 20.0, 10th for the week. Dallas (October 5: Battle Lines, rating 24.7) was #1, The Cosby Show (October 4: Bad Dreams (episode 3), rating 21.9) was 5th, Knots Landing (October 4: Buying Time (season 6 premiere), rating 21.1) was 7th; and Murder, She Wrote (October 7: Deadly Lady (episode 2), rating 20.3) was 9th. No Dynasty on October 3.
October 12, 1984: Strangers, rating 18.5, 17th for the week. Dynasty (October 10: The Mortgage, rating 25.1) was 5th, Dallas (October 12: If at First You Don't Succeed, rating 24.0) was 7th, The Cosby Show (October 11: Is That My Boy? (episode 4), rating 20.6) was 9th; and Murder, She Wrote (October 14: Birds of a Feather (episode 3), rating 19.4) was 12th. No Knots Landing on October 11.
October 19, 1984: The Outcasts, rating 19.4, 14th for the week. Dynasty (October 17: Fallon, rating 26.1) was #1, Dallas (October 19: Jamie, rating 24.6) was 2nd, The Cosby Show (October 18: A Shirt Story (episode 5), rating 21.3) was 7th, and Knots Landing (October 18: Calculated Risks, rating 19.7) was 13th. No Murder, She Wrote on October 21.
October 26, 1984: Shadows, rating 19.9, 13th for the week. Finished ahead of Murder, She Wrote (October 28: Hooray for Homicide (episode 4), rating 19.7, 15th). Dynasty (October 24: The Rescue, rating 26.3) was #1, Dallas (October 26: Family, rating 25.9) was 2nd, The Cosby Show (October 25: Breaking with Tradition (episode 6), rating 21.2) was 8th, and Knots Landing (October 25: Hanging Fire, rating 20.5) was 9th.
November 2, 1984: Lord of the Valley, rating 21.9, 4th for the week. Finished ahead of The Cosby Show (November 1: One More Time (episode 7), rating 20.0, 8th), Knots Landing (November 1: A Little Help, rating 19.2, 11th); and Murder, She Wrote (November 4: It’s a Dog’s Life (episode 5), rating 16.9, 23rd). Dallas (November 2: Shadow of Doubt, rating 27.1) was #1 and Dynasty (October 31: The Trial, rating 24.9) was 2nd.
November 9, 1984: The Intruder, rating 21.1, 8th for the week. Finished ahead of Knots Landing (November 8: Ipso Facto, rating 19.4, 11th). Dallas (November 9: Homecoming, rating 26.2) was #1, Dynasty (November 7: The Verdict, rating 25.7) was 2nd, and The Cosby Show (November 8: Play it Again, Vanessa (episode 8), rating 21.2) was 7th. No Murder, She Wrote on November 11.
November 16, 1984: Pain and Pleasure, rating 20.5, 11th for the week. Finished ahead of Murder, She Wrote (November 18: Lovers and Other Killers (episode 6), rating 19.1, 16th). Dallas (November 16: Oil Barons Ball III, rating 26.5) was 2nd, Dynasty (November 14: Amanda, rating 23.5) was 5th, The Cosby Show (November 15: How Ugly is He? (episode 9), rating 22.5) was 6th, and Knots Landing (November 15: Truth and Consequences, rating 20.7) was 10th.
November 23, 1984: The Trump Card, rating 18.8, 11th for the week. Finished ahead of The Cosby Show (November 22: Bonjour Sondra (episode 10), rating 16.7, 18th) and Knots Landing (November 22: Love to Take You Home, rating 16.3, 22nd). Dynasty (November 21: The Secret, rating 24.3) was 3rd, Dallas (November 23: Shadows, rating 22.6) was 5th; and Murder, She Wrote (November 25: Hit, Run and Homicide (episode 7), rating 19.7) was 9th.
November 30, 1984: Tarantella, rating 21.1, 12th for the week. Dallas (November 30: Charlie, rating 25.9) was 2nd, Dynasty (November 28: Domestic Intrigue, rating 25.2) was 3rd, and Knots Landing (November 29: Tomorrow Never Knows, rating 21.4, rating 21.4) was 11th. The Cosby Show was a repeat on November 29. No Murder, She Wrote on December 2.
December 7, 1984: Going Once, Going Twice; rating 20.7, 12th for the week. Finished ahead of Knots Landing (December 6: We Come Together, rating 20.2, 18th). Dynasty (December 5: Krystina, rating 25.3) was #1, Dallas (December 7: Barbecue Five, rating 24.7) was 3rd, The Cosby Show (December 6: You're Not a Mother Night (episode 11), rating 23.1) was 4th; and Murder, She Wrote (December 9: We're Off to Kill the Wizard (episode 8), rating 22.3) was 6th.
December 14, 1984: The Triumvirate, rating 20.4, 14th for the week. Finished ahead of Knots Landing (December 13: Message in a Bottle, rating 20.3, 15th) and Murder, She Wrote (December 16: Death Takes a Curtain Call (episode 9), rating 16.2, 30th). Dynasty (December 12: Swept Away, rating 26.5) was #1, Dallas (December 14: Do You Take This Woman, rating 25.2) was 2nd, and The Cosby Show (December 13: Rudy’s Sick (episode 12), rating 21.3) was 6th.
December 21, 1984: Winner Take All, rating 18.4, 16th for the week. Dynasty (December 19: That Holiday Spirit, rating 25.9) was #1, Dallas (December 21: Déjà Vu, rating 23.0) was 4th, The Cosby Show (December 20: Father’s Day (episode 13), rating 21.7) was 6th, and Knots Landing (December 20: Distant Locations, rating 20.9) was 7th. Murder, She Wrote was a repeat on December 23.
December 28, 1984: Suitable for Framing, rating 21.2, 8th for the week. Finished ahead of Knots Landing (December 27: Uncharted Territory, rating 20.3, 10th). Dallas (December 28: Odd Man Out, rating 24.5) was #1 and Murder, She Wrote (December 30: Death Casts a Spell (episode 10), rating 22.3) was 6th. No Dynasty on December 26. The Cosby Show was a repeat on December 27.
January 4, 1985: Vicious Circle, rating 21.5, 13th for the week. Finished ahead of Knots Landing (January 3: Weighing of Evils, rating 21.4, 14th). Dallas (January 4: Lockup in Laredo, rating 26.3) was 3rd, Dynasty (January 2: The Avenger, rating 26.2) was 4th; and Murder, She Wrote (January 6: Capitol Offense (episode 11), rating 22.4) was 9th. The Cosby Show was a repeat on January 3.
January 11, 1985: Insult and Injury, rating 21.8, 7th for the week. Tied Murder, She Wrote (January 13: Broadway Malady (episode 12), rating 21.8, 7th). Finished ahead of Knots Landing (January 10: #14 With a Bullet, rating 18.6, 23rd). Dallas (January 11: Winds of War, rating 27.8 (season high)) was #1, Dynasty (January 9: The Will, rating 27.7 (season high)) was 2nd, and The Cosby Show (January 10: Independence Day (episode 14), rating 25.4) was 3rd.
January 18, 1985: Pre-empted for Any Which Way You Can. The Cosby Show (January 17: Physician of the Year (episode 15), rating 27.9) was 3rd, Dynasty (January 16: The Treasure, rating 27.0) was 4th, and Knots Landing (January 17: Inside Information, rating 20.4) was 14th. No Dallas on January 18. Murder, She Wrote was a repeat on January 20.
January 25, 1985: Acid Tests, rating 20.0, 16th for the week. Dallas (January 25: Bail Out, rating 26.1) was #1, Dynasty (January 23: Foreign Relations, rating 25.0) was 3rd, and Knots Landing (January 24: Out of the Past, rating 21.3) was 10th. The Cosby Show was a repeat on January 24. No Murder, She Wrote on January 27.
February 1, 1985: The Showdown, rating 20.1, 16th for the week. The Cosby Show (January 31: Jitterbug Break (episode 16), rating 27.8) was #1, Dynasty (January 30: Triangles, rating 27.0) was 2nd, Dallas (February 1: Legacy of Hate, rating 26.2) was 3rd, Knots Landing (January 31: Lead Me to the Altar, rating 22.9 (tied for season high)) was 8th; and Murder, She Wrote (February 3: Murder to a Jazz Beat (episode 13), rating 22.0) was 11th.
February 8, 1985: Retribution, rating 20.3, 13th for the week. Finished ahead of Murder, She Wrote (February 10: My Johnny Lies Over the Ocean (episode 14), rating 19.9, 16th). The Cosby Show (February 7: Theo and the Joint (episode 17), rating 26.1) was #1, Dynasty (February 6: The Ball, rating 25.9) was 2nd, Dallas (February 8: Sins of the Fathers, rating 25.0) was 4th, and Knots Landing (February 7: Fly Away Home, rating 21.9) was 10th.
On a win/loss/tie basis, the first 19 episodes of the season scored 1-16 vs. Dynasty, 3-12 vs. new episodes of The Cosby Show, 6-7-1 vs. new episodes of Murder, She Wrote; and 8-9 vs. Knots Landing.
February 15, 1985: Forsaking All Others, rating 19.4, 17th for the week. The Cosby Show (February 14: Vanessa’s New Class (episode 18), rating 26.6) was #1, Dallas (February 15: The Brothers Ewing, rating 25.0) was 2nd, Dynasty (February 13: Circumstantial Evidence, rating 23.4) was 5th, Knots Landing (February 14: Rough Edges, rating 20.7) was 11th; and Murder, She Wrote (February 17: Paint Me a Murder (episode 15), rating 20.5) was 13th.
February 22, 1985: Recriminations, rating 20.2, 15th for the week. Finished ahead of Knots Landing (February 21: The Emperor's Clothes, rating 18.8, 21st). Dallas (February 22: Shattered Dreams, rating 25.8) was #1, The Cosby Show (February 21: Clair’s Case (episode 19), rating 25.1) was 3rd, Dynasty (February 20: The Collapse, rating 24.6) was 4th; and Murder, She Wrote (February 24: Tough Guys Don't Die (episode 16), rating 21.7) was 11th.
March 1, 1985: Pre-empted for The Wizard of Oz. The Cosby Show (February 28: Back to the Track Jack (episode 20), rating 27.0) was #1, Dynasty (February 27: Life and Death, rating 24.8) was 2nd, Dallas (March 1 (10 pm): Dead Ends, rating 22.6) was 7th; Murder, She Wrote (March 3: Sudden Death (episode 17), rating 21.6) was 9th; and Knots Landing (February 28: The Deluge, rating 20.3) was 13th.
March 8, 1985: House Divided, rating 17.5, 22nd for the week. Dynasty (March 6: Parental Consent, rating 24.0) was 3rd, Dallas (March 8: Trial & Error, rating 22.4) was 6th, Knots Landing (March 7: A Piece of the Pie, rating 20.4) was 11th; and Murder, She Wrote (March 10: Footnote to Murder (episode 18), rating 19.7) was 12th. The Cosby Show was a repeat on March 7.
March 15, 1985: The Trial, rating 17.6, 20th for the week. The Cosby Show (March 14: The Younger Woman (episode 21), rating 28.3) was #1, Dynasty (March 13: Photo Finish, rating 24.2) was 2nd, Dallas (March 15: The Verdict, rating 22.7) was 5th; and Murder, She Wrote (March 17: Murder Takes the Bus (episode 19), rating 22.4) was 6th. No Knots Landing on March 14.
March 22, 1985: Pre-empted for NCAA Basketball. Dynasty (March 20: The Crash, rating 22.6) was 3rd and Knots Landing (March 22 (9 pm): The Forest from the Trees, rating 16.0) was 29th. The Cosby Show was a repeat on March 21. No Dallas on March 22. Murder, She Wrote was a repeat on March 24.
March 29, 1985: Justice for All, rating 19.2, 15th for the week. The Cosby Show (March 28: The Slumber Party (episode 22), rating 30.1 (season high)) was #1, Dynasty (March 27: Reconciliation, rating 23.1) was 5th, Dallas (March 29: Sentences, rating 23.0) was 6th; Murder, She Wrote (March 31: Armed Response (episode 20), rating 21.2) was 10th, and Knots Landing (March 28: A Man of Good Will, rating 19.4) was 14th.
April 5, 1985: Pre-empted for Stormin’ Home. Dynasty (April 3: Sammy Jo, rating 23.1) was 3rd; Murder, She Wrote (April 7: Murder at the Oasis (episode 21), rating 20.4) was 5th; and Knots Landing (April 4: For Better, for Worse; rating 18.2) was 13th. No The Cosby Show on April 4. No Dallas on April 5.
April 12, 1985: Devil’s Harvest, rating 18.5, 19th for the week. Dynasty (April 10: Kidnap, rating 24.5) was 2nd, Dallas (April 12: Terms of Estrangement, rating 22.1) was 6th, and Knots Landing (April 11: Four, No Trump; rating 19.9) was 11th. The Cosby Show was a repeat on April 11. No Murder, She Wrote on April 14.
April 19, 1985: The Decline, rating 16.9, 17th for the week. Murder She Wrote (April 21: Funeral at Fifty-Mile (season 1 finale), rating 24.5 (season high)) was 2nd and Dallas (April 19: The Ewing Connection, rating 21.1) was 5th. No Dynasty on April 17. The Cosby Show was a repeat on April 18. No Knots Landing on April 18.
April 26, 1985: Pre-empted for Arthur the King. No Dynasty on April 24. The Cosby Show was a repeat on April 25. No Knots Landing on April 25. No Dallas on April 26.
May 3, 1985: And the Fall, rating 18.3, 6th for the week. Finished ahead of Knots Landing (May 2: A Price to Pay, rating 17.8, 9th). The Cosby Show (May 2: Mr. Quiet (episode 23), rating 25.5) was #1 and Dallas (May 3: Deeds and Misdeeds, rating 21.4) was 3rd. No Dynasty on May 1.
May 10, 1985: Cold Comfort, rating 19.1, 8th for the week. The Cosby Show (May 9: Cliff’s Birthday (season 1 finale), rating 24.1) was #1, Dallas (May 10: Deliverance, rating 22.6) was 2nd, Dynasty (May 8: The Heiress, rating 21.9) was 3rd, and Knots Landing (May 9: One Day in a Row, rating 19.2) was 7th.
May 17, 1985: Confessions, rating 22.0, 4th for the week. Finished ahead of Knots Landing (May 16: Vulnerable, rating 20.2, 6th). Dallas (May 17 (8:30-10 pm): Swan Song (season 8 finale), rating 27.5) was #1 and Dynasty (May 15: Royal Wedding (season 5 finale), rating 25.9) was 2nd.
May 24, 1985: The Avenging Angel (season 4 finale), rating 16.4, 12th for the week. Knots Landing (May 23: The Long and Winding Road (season 6 finale), rating 22.9 (tied for season high)) was #1.
On a win/loss basis, the remaining 11 episodes scored 3-6 vs. Knots Landing.
Dallas weakened as a lead in starting March 1985 and that also played a part in the ratings drop during the final 11 episodes of the season.