Help please wall marked by wallpaper scr?

My dad has been painting the hallway and we took the wallpaper off but the scr left gashes in the wall so he sanded it, then put two coats of paint on it, then filled the marks with the white-putty like stuff, then painted it over again, and you can still see the marks and the putty. How many coats will it take to cover the putty stuff so it doesn't look patchy in the light and so it will look normal, or will he just have to sand the whole wall again and paint the wall from scratch? Thanks for your help oh and it's a pale yellow color if it makes a difference