no mint mark would mean it was minted in the Philadelphia mint. Halves minted in Philly had no mint mark until 1980, when they added the P mint mark on the obverse in the same location as the D.
I can't visualize the other things you mention, but I'm inclined to guess damage. Could you post a picture of your coin?
I can't visualize the other things you mention, but I'm inclined to guess damage. Could you post a picture of your coin?




















