I have quite a few 1957 D's with the bottom of the B or 9 filled in or mounded. My on line readings would suggest it's a common error. However, I have one that might qualify for a BIE. There is also a little bit of action along the left leaf on the reverse. .
Don't want to burst your bubble, but it looks to be just a common die chip. You might be able to find someone who wants to pay a little extra for it, but, as far as I know, it doesn't really have any added value.