Factory Tint mostly comes on SUV’s & Crossover vehicles behind front doors and aftermarket tint is so different that it shouldn’t both be called TINT. Vehicles Factory tint is smoked within the glass itself, mostly in charcoal/black color. Professional aftermarket tint is a film that is installed internally over the glass, it can be peeled and reapplied. If you’re purchasing your vehicle used, the previous owner might have vehicle windows tinted with an aftermarket film or over the factory smoked glass. To determine the difference, you have to roll the window halfway down and look at the top edge of the window for an overlap or 1/8” gap.
Because factory smoked glass is inside the window and aftermarket film is applied inside of the window, it’s more than possible to place aftermarket film on top of factory tint.