Best to stick with one coin at a time.
The first coin looks corroded to me. A nontechnical term you may see used on here is "staining". What I suspect in cases like yours is a type of corrosion called dealloying. Remember that the clad layer is mostly copper—not clad—to begin with. 75%/25% Cu/Ni, to be more specific. Corrosive environments which remove nickel and/or replate copper back onto the surface could make it look copper colored. In industrial environments, that type of dealloying is called denickelification. I doubt that it has been studied on coins. Not enough money involved.
(Yes. That pun was intentional, but likely true. )
Signs that this might be the case:
1. Copper color doesn't seem dark enough to be just core layer. Core is pretty much pure copper.
2. Rough, pitted appearance of surfaces = corrosion
3. Weight is only a little under spec, so wear and corrosion seem to explain it, although I have seen a Mike Diamond article that says a clad layer can be missing without a noticeable low weight, but that type of missing clad error is really rare. Otherwise, two clad layers missing would be much lower.
4. Unless it is just glare, there seems to be some paler spots on the high points which indicates the dealloyed layer has been worn through into the undisturbed cupronickel cladding.