What is the question? If the MC is wet location rated, doesn't that encompass damp locations?
I looked at the MFG page for the Southwire MC-XHHW (one of the wet location MCs), it says that is an XHHW-2 conductor and that conductor is listed wet and damp (330.10(A)11(c)). I assume you would derate from the 75c column in a damp location like you do in a wet one.
