In this post I'll list the reprints and/or variants of which I'm aware for 1942 and part of 1943. If the covers are different for the printings both are provided. Books 51 and 52 are the only reprints with different covers. After that, until book 86, Collins used the same illustration but changed the colour scheme. All later reprints, with one exception, used the same cover.
1942 - first fifty books - no known reprints.
1943 - books 51-72 - these are the spring books (from a Quill & Quire May 1943 ad by Collins):
51 - Immortal Sergeant by John Brophy - stated reprint 1944.
52 - Steady as You Go by Bartimeus - reprint not stated. The first printing's yellow cover is shown in the May 1943 ad for Spring books. The second printing's cover is by Margaret Paull who didn't start her work at Collins until the fall books beginning with 74.
60 - Six Feet of Dynamite by Berkeley Gray - stated reprint 1945.
65 - The Knife by Herbert Adams - reprint not stated. The address on the reprint is 70 Bond St. in Toronto which wasn't used by Collins until late 1944. The first printing has the 48 Pall Mall London address used in 1942 through late 1944.