Alan, thanks for the compliment! I find all this fascinating. I got my info from Suskin’s book. It’s of course possible that Bennett wrote the dance music, but it’s hard to imagine that he would have spent that sort of time with Agnes de Mille and her dancers! That ballet changed Broadway history, and it’s astonishing to me that nobody knows who put the music together, all 521 bars of it!
I suppose what’s most likely is that Morgan Lewis used Rodger’s melodies during rehearsal, filled in as best he could, and then Bennett fixed it up when he orchestrated.