I only know the story as Butch' s mother Ruby told me. Harvey Reavis took Billy to the Johnson's and they adopted him. Billy was the fifth child of Harvey & Minnie. The children in order of birth are Marie, Thurman, Ruth, Charlie and Billy. I'm sure that if Harve could have made Ruth stay home to take care of Billy, they wouldn't have had to let him go. I don't know how long Minnie was sick but I would think for a while according to the illness she had.
Thurman & Rubys children are in order of birth Charles Robert, Virginia Lee, Edward Wayne, Thurman Lee Reavis Jr (butch), Nancy Jean, Linda Ray, Nina Fay, Donna Ophelia & Gary Don. They are all still living except for Charles Robert who was hit by a car when he was about eleven. Charlie and Lilly's children are Marilyn Kay, Ricky Charles & Billy Joe.
The only thing that might be possible about the box car is that Harve May have taken Billy in a box car to meet the Johnson's otherwise I think the story may have evolved as stories tend to do. Oh, and was my husband's father Thurman that worked in the field beside his dad Harvey.