A larger D mm was used for this year per the Guide Book of Lincoln Cents. I'm wondering if it could be a large D over small D. Not really sure though. Good find.
Hate to be the possible bearer of bad news but it looks to me like it is the early stages of zinc rot. sometimes the coin gets a split in the copper just below the mint mark when it is struck, air gets in and the rot begins. Look at it under high magnification to see if there is any sign of this Richard
