I think other sources sometimes call Millennials Generation Y. I am using a company that presents/focuses on this stuff so there isn't argument and conflict over the boundaries. There are a lot of different definitions of the groups, and even more terms out there.
I've also seen a Gen X, Gen Y, and Millennials are separate designations, although I don't know if it matters and I'm not arguing with the classifications you've outlined. I think anyone on the ends of those designations (the buffer zones) is going to have a more mixed experience.