I bought the 3 step sample kit in 2012 to do the bottom edges of the doors on my crew cab truck. The insides of the bottom edges are starting to rust. I ordered the it with the black top coat. Question one is, is this kit still good or does it have a shelf life? I have never opened it and it has been in the basement, so it has never froze. Question two is, if the sample kit is still good, can I order just a sample size can of the off white to use with my sample kit I already have instead of using the black I bought a couple years ago?