Can't be a cracked die because it is incuse. Can't be lamination because so far I've found two of this same die from this roll. Struck through something that hung along for the ride for a few strikes?
This thread should help I hope http://www.cointalk.com/t50835/#post562459 !956-D & few 1957-D have a shadowed D that almost at the bottom of Abe's coat hard to find in gem Bu
I remember asking about these years ago and was told it was struck thru some type of slag or hardened material that stuck fast to the die. Was also told it was stuck fast for a long period of time because they seem to be quite common on 57- D's...
Abe- I wonder if it was done to a working hub. Were the ones you saw like this one or was the struck through in a different area?
I can't say for sure right now I'd hane to go thru 100's of them to find out. I know it was on the obverse and in the same general area...