I am knowledgeable about metals as I am an Engineer, and I sell corrosion resistant metals. First, I would not use the wording of cathodic protection. Cathodic protection in my circle of corrosion control is about stopping the transfer of electrons in a corrosion reaction. This works well in your household hot water heater or your Evinrude outboard motor on your boat. Here zinc is used to corrode first and produce an electric current that prevents your important metal from corroding. If you are protecting a long pipeline, you can introduce an electric current to prevent corrosion. (PS this works when your metal is submerged in an electrically conductive solution like unpure water I have seen Cathodic protection devices for sale for your vehicle, but this will best protect your metal when submerged at the bottom of the lake.) The spray coating is a good corrosion protector. Coatings are subject to fail if it does not bond well. Surface preparation is essential on most adhesives coatings. Concerns could be that the coating premature fails because the coating did not bond well. As for sealing rust or road grim under the coating, this IS a common corrosion issue. I have read corrosion case study like a bridge being built with wire stays. The bridge took 3 years to build. The wire ropes were stranded on site. Then the cable was sealed in the salty air and even wet with rain still on the steel. The iron oxide was visible before being coated. The coating was to prevent corrosion but since the steel was contaminated, the structure had a 10-year life instead of 50 years. Bottom line is the life expectancy due to corrosion has been shortened, but to what degree will be arguable. There is probably a guide from the maker of the protective coating that would state how to properly prepare the surface before the coating is applied that your lawyer would use to show fault with the coating applicator. Good luck. I am just glad that the metals used on my Gen1 Raptor are better at corrosion resistant than some of that steel that rusts thru seen on 20-year-old trucks.