S&G tended to include the "missing" verse in live performances, though, e.g. The Concert in Central Park from the early 80s. Art was completely off his face... :-)
The common wisdom is that Paul Simon was severely irritated by the credit given to Art for song-writing on songs like Bridge Over, because Art sang the lead vocal.
Personally, I could die a happy man if I had written any of the songs Paul Simon has composed, and I would be secure in the knowledge that I wrote them, and that my friend with the beautiful voice gave life to them, but then, I'm not Paul Simon.