Reilly's postcard to Caryll Houselander is franked with an Imperial Russian postage stamp. The Union of Soviet Socialist Republics (USSR) was established in 1922. All imperial postage stamps for sale would have been replaced with stamps of the USSR.
Reilly sings "When the Red, Red, Robin Comes Bob, Bob, Bobbin Along" in November 1925, but the song was not written until 1926.