The last of Beaver's three books, Cherchez la femme?, was published in December 1941. There is a note in the back that says:
"Our 'service' pocket library editions are now in circulation [and] are obtainable in boxed sets of the three titles. Red for the Navy, Blue for the Air Force and Khaki for the Army."
This is interesting because there are also variants of each book with illustrated covers. This note suggests that the illustrated covers were the retail issues and the text cover issues were published later as service editions only. I had thought that, like the LA Bantams and Red Arrows, the Beaver illustrated versions came after the text versions in order to boost sales. I've never seen the illustrated versions so I wonder if this note is in Cherchez la femme?.