According to Ken Mendelbaum in his book Not Since Carrie, Jerome Robbins worked on the show for two weeks in Boston.
The show was losing money before it opened on Broadway. The producers posted a closing notice on opening night, however Anthony Brady Farrell, the owner of the theatre, decided to put his money into the show to keep it going.
With the show losing money, the leads were all asked to take paycuts. Several declined, including Thelma Carpenter, Jane Kean (oddly), and Mark Dawson. In an artcile dated August 6, 1955 in The Afro-American, Thelma Carpenter's refusal was the week prior (July 24-July 30), suggesting that the new cast would have started on August 1, 1955. We have used this date as the start date for their replacements, however it is entirely possible that Virginia Martin and Karen Shepard (already the understudies) filled in while they rehearsed Georgia Reed and Virginia Dandridge.