At least 57 books were published by a company called Readers' League of America Inc, a New York publisher. I haven't been able to find any information about Readers' League.
An example is The "Canary" Murder Case by S.S. van Dine. The pictures below show the differences in the covers. Other differences are:
1) on the title page the publisher is changed from "POCKET BOOKS INC. [logo - Gertrude] NEW YORK, 20. N.Y." to "ARMED SERVICES EDITION | READERS' LEAGUE OF AMERICA | NEW YORK, N. Y."
2) on the copyright page of the ASE the printing history has been removed.
Pocket 248 - November 1943
Pocket 248 back
Pocket [248] ASE - no date
Pocket [248] ASE back