Forgive, but I will have to pee on this assessment (just a sprinkle). SOME of the older Paiste cymbals are just a tad thinner than the later ones. When they would restructure a cymbal line, the designation would sometimes change ... even though it was the same cymbal. I have had several 18, 19, and 20 inch crashes throughout the years and they were not all the same weight and thickness ... the variable being time point of manufacture. The older ones were just a bit thinner (lighter) than the later ones. The designations floated a bit within the 2002 line.
There are those that will staunchly deny or refute this (some can be downright rude), but it did happen from time to time. It goes against the "Master Cymbal" concept, but they adapted ever so slightly to the changing music trends. They kept it in the very high 90's, but they were not 100% across the board ... nor should we expect them to be.