I've mentioned in a couple of posts that Wm. Collins Sons & Co. Canada Ltd. published 459 of their White Circle imprint. This is the number they published in their consecutively numbered series that ended with number 545 (actually C.D. 545X). However Collins also published two other paperbacks with the White Circle name that were not part of this series.
The first is a real odd-ball. Dear Sir; by Juliet Lowell was a collection of letters written my Americans during WWII. It was published in the US in 1944 in hardcover and paperback. Then, as S4, by Collins in 1945. It is described on the front cover as "A White Circle Pocket Edition" and has ads for other White Circles. But the publisher is North Star which was an imprint of Collins (see post of October 22). Collins isn't mentioned in the book. Collins also published Dear Sir; as a hardback without any reference to White Circle on the front cover.
Below is the White Circle edition and the American paperback edition published by Eagle Books of New York.