An interesting snippet from Wikipedia:
"It has been rumoured that while Bernstein was off trying to fix the musical Candide, Sondheim wrote some of the music for West Side Story, and that Bernstein's co-lyricist billing mysteriously disappeared from the credits of West Side Story during the tryout, presumably as a trade-off. However, Suskin writes in Show Tunes that "As the writing progressed and the extent of Bernstein's lyric contributions became less, the composer agreed to rescind his credit. ... Contrary to rumour, Sondheim did not write music for the show; his only contribution came on "Something's Coming", where he developed the main strain of the chorus from music Bernstein wrote for the verse"
Fortunately, for all of us, Sondheim went on to establish himself as a peerless composer of musicals.
The final curtain has fallen on a life, well-lived. Rest well, Sir...you've earned it.