All the triangle shaped knob indicates is that the cylinder/valve it came from was equipped with an OPD valve. Your ASME tank has one also, but it's a different type used on the separate fill port instead of the service valve where the handle goes. As said, not likely they'll even notice, but no harm done even if they do. If you really want one of the round style knobs, most LP bulk dealers usually have a bunch of junk pre-OPD cylinders piled up somewhere that I'm sure they'd let you pull one off of.