Throughout his life, Bernstein wrote short pieces dedicated to his friends, which he called Anniversaries. Bernstein borrowed from himself: a few of the Anniversaries are incorporated into the Serenade.
The most obvious are Elizabeth Rudolf and Lukas Foss, which appear in Aristophanes…
…Elizabeth Ehrman which forms the jazzy basis of the Alcibiades part of Socrates:Alcibiades…
…and Sandy Gelhorn, which appears in the “B” section of the second part of the first movement, Phaedrus:Pausanius
Less obvious: Listening to the beginning of Serge Koussevitsky foreshadows the opening melody of the Serenade, and William Schuman reminds me a bit of Erychimachus.
(These Spotify links seem to take a long time to load, sorry! If you are having trouble, go directly to Spotify and search Bernstein Anniversaries)