The "Oreo-cookie" effect in that fourth photo is always a dead giveaway for chemical damage -- the softer copper gets etched away more quickly than the harder cupronickel layers, even though nickel itself is more reactive than copper. The red showing in the first and second shots looks like exposed copper, but I wonder if it's something on the surface of the coin. There's certainly plenty of other discoloration.
ED, environmental damage. It looks like that last one was in some acidic solution and it ate the copper. The others could have also been in mild acid that removed the clad. Just a guess on my part.
