They are, but the number you speak of is specific to the model year. For example, in the U.S., the 2003-2005 Evos are all Evo VIIIs, while the 2006 models are IXs.
However, there are some older Evos that made their way to the U.S. through people importing them through private companies that do so legitimately. I actually saw an Evo IV on the road a week ago in my area.