It appears to be a lamination. This is caused, and correct me if I'm wrong, by impurities under the metal that separated the piece that is now gone.
Imagine this. You have that lamination thing on the back of the coin covering the bottom and on the front it was a 1909-s. The torture of not knowing if it was a 1909 s vdb would kill me.
You can put that worry out of your mind if there is no VDB on the reverse. And, if there is VDB on the truncation of Lincoln's bust, you can stop worrying if it may be a 1914-D.
