The Mystery League, Inc. was an early 1930s publisher of mysteries/thrillers. Only 30 were published. The series was distinctive for two reasons - the books were sold in a drug store and a cigar store chain for 50 cents, less than the going hardcover price and the dust jackets, which is the main reason they are collectible.
The Mystery League series shares three authors with Harlequin Books. Here's the first - Frances Shelley Wees with one Mystery League and two Harlequins.
The Scottish-British publisher Wm. Collins Sons & Co. published paperbacks in the 1940s and 1950s in a number of countries, including India. The Indian editions were unnumbered and came in different series. Here are two examples. Never a Dull Moment is digest sized (12.5cm x 18.3cm) and has a dustjacket glued at the spine over blank white covers. TheBody in theLibrary is mass market sized. Both are published by W.A.R. Collins, the first in Calcutta (1946), the second in Bombay (undated).
I recently found an ad in a 1950 issue of Maclean's that solved a Harlequin artist mystery. Earlier this year I discussed an artist who signed his two Harlequin covers as "NMR". And here I discussed an artist who signed his work as "Ralph". I speculated that this was Max Ralph. Now I know the two artists are N. Max Ralph. The Maclean's ad notes that the art is the work of "N Max Ralph" and the signature is clearly the same. There is also a third signature - "R". Why three different ways of signing his work? Here are examples of each plus the ad.
Wm. Collins Sons & Co. Canada Ltd published 459 books in their White Circle numbered series between 1942 and 1952. But there were also a handful of paperbacks designated White Circle in the 1940s through the 1970s that were not part of this series. Here are two from the 60s. While published five years apart they are consecutively numbered. I don't know if there is a A1002.