I recently had the hardwood floors in my hallway well covered with tarps as I drywalled the room. After finishing, removing the tarps and cleaning the floors several times, to my horror I have noticed light colored spots in some areas and dull spots elsewhere. The light colored spots look as though they penetrated the polyurethane. Did the drywall dust do this? Do I need to have my floors sanded again. I just had them refinished 9 months, which adds to the anguish.