I believe they are from 1940 to early 1942, although Steve will be able to confirm this. The Gladiator, for example, was still in use in 1941 in the Western Desert, and the Blenheim there and in Europe until late 1942. The Walrus served throughout WW2. Other obsolete types, like the Hart/Fury and transports such as the Bombay, also served as communications aircraft for many years.