I have never found a cud American coin, but looking through some random coins, I saw this: Would this constitute a cud?
My thought is die chip. Cuds are caused by a broken die and although that does touch the rim it doesn't look like a broken die caused it.
After I looked at the picture, that's what I started to think. Could a die-chip be the start of a die break that would produce a cud?
If there is evidence of a die crack running between the blobs of metal, then yes it could be the start of a pre cud