Conversation so far:
What happened in the late 1930s for Duke Ellington?
From 1936, Ellington began to make recordings with smaller groups drawn from his then-15-man orchestra and he composed pieces intended to feature a specific instrumentalist.
Who was a part of the group Duke Ellington worked with in the later 1930s when Ellington was more focused on composing to feature a specific instrumentalist?
Billy Strayhorn, originally hired as a lyricist, began his association with Ellington in 1939.

Question: did they produce any music?
Self-contained rewrite: Did Duke Ellington produce any music with Billy Strayhorn?