Qualify the surface before choosing the coating
Restoration begins by qualifying the roof, not by choosing a bucket of coating. The membrane and any previous coatings need to be compatible with the proposed system. Surface contamination and weathering can affect preparation and adhesion.
Moisture below the surface is a different problem from a dirty surface. Wet or damaged insulation must be dealt with as part of the scope, and an unsound deck cannot be made suitable by coating over it. A roof that needs extensive removal may be better considered for replacement.