One, nickels do not have clad layers so it can't be missing one. Two, Yes an acid soak would compromise the luster, so it probably isn't acid soaked. One possibility would be a planchet that skipped the cleaning step after being annealed. The annealing can caiseoxide layers to form on the planchet giving it a darkened rough appearing texture that would still show after striking, but the metal movement during the strike will still form luster on the coin.
