Daniel, I'll go back and bone up on this.
I had thought the other two were also fitted with blind drivers.
But I could be mistaken, you site a great source. Thanks for the info, but I am not mistaken about how long the practice had been around and that it was not used because of the worn rail, but rather in an attempt to wear them even more by allowing more surface adhesion. Two former C&S enginemen told me that the C-19's could barely pull themselves up the C&S grades compared to "their regular engines".
I don't believe #537 was fitted with half flanges either, now that I think about it, so you are probably right.
Mike