The Big 4

From Author Wars - https://authorwars.com/publications/the-big-4-567595.html

Overview:

Title: The Big 4
Author: Agatha Christie
Year: 1961
Publisher: Avon
Price: $0.35
Pages: 126
Binding: Paperback
Type: Novel
Title Reference: The Big 4
Notes:
- The title stated as "The Big 4" on the front cover, title page, and spine.
- The publication date is not stated. The publication is dated 1961-00-00 based on the catalog number. Dating clues from the advertising at the back of the book are:
  - Ad on page [127] for Avon T485 Clean Crimes and Neat Murders by Henry Slesar that includes "1959 winner of the Mystery Writers of America Award". Wikipedia reports 1960 for this edition though does not give a source for the date.
  - Ad on page [128] for Avon G1054 Station Wagon in Spain by Frances Parkinson Keys. This was first published in 1959 though Abebooks sellers report that Avon G1054 was published in 1960.
  - The publisher is stated on the title page as "Avon Book Division" over "The Hearst Corporation". The publisher name is not on the copyright page. This has been normalized to "Avon" for ISFDB.
  While the advertising points to a 1960-00-00 publication date we have publications for Avon T-289 to T-371 for 1959, Avon T-380 to T-483 for 1960, and Avon T-524 for 1961. The T series (35¢) was not used after 1961. This publication is T-526 which puts it early in 1961.
- The cover art is not credited.