QcCowboy

actually, they err on that website, since Victory at Sea is not a symphony either... it's the score to a television series.

and just in case anyone doubts it:

Victory at Sea: television series IMDB page

Article on Richard Rodgers' score

The latter article actually removes a tiny bit of credit from Richard Rodgers, since much of the music was arranged and/or orchestrated by Robert Russell Bennett.
I remember this from having owned a vinyl pressing of this score. I also remember having another disk of music by Robert Russell Bennett, who was a very fine orchestrator and composer in his own right.

So, I guess R. Murray Schaffer is still the holder of the title.
Like I said, technically, however, "Ra" is not a symphony. However, it IS a single piece of music, meant to be performed in one sitting.