it is zinc rot and you need to start your own threads for your coins , this is confusing with different coins on one thread
If you look closely at the first coin you will see that there is a hole in the plating. The zinc underneath has rotted out and the thin copper plating has been flattened as a result.
I agree, good analysis. Just think how few of these pieces of crud cents will survive in the future. Most I have seen found with metal detectors are already corroding away. None will survive except those saved by collectors it seems.
it could be something else if it were a clad coin or copper cent, but zinc rots easily, and anything trapped under the copper plating can start the zinc to rot, see here for planchet errors http://error-ref.com/part-v--planchet-errors.html, i've found plenty zinc cents rotting away while roll hunting, heres a recent find,
search the web for "minting process" an familurize yourself on how coins are made, it will help you pick out things like post mint damage a lot easier once you understand the minting process,