I haven't read the report fully, but when I glanced at it, I noticed that they described Millennials as those born after 1977. This was the same definition that I saw in the William E. Smith report on generations from a few years ago. The Smith report (if I remember correctly) had Baby Boomers as 1946-64 (18 years), Generation X 1965-76 (11 years) and Millennials as 1977-forever (currently up to 32 years!).
These definitions root the generations in demographic data. That is, Boomers are people born literally during the boom in birth rates after World War Two, Generation X are born during the dip in birth rates after that, and Millennials are people born any time after that. I get that this is an objective justification for the cutoff dates (and I imagine quantitative researchers like objective parameters), but I don't think it really has anything to do with generations.
Generation X is different from Baby Boomers NOT simply because fewer babies were born during their birth years. That is one factor, but the primary difference is the fact that Generation X grew up in the late 1970s and 1980s, as opposed to the 1960s and early 1970s. If you were born in 1964, you pretty much missed "the sixties." You'll have early memories of them, of course, but your real coming of age was later. That's why you're Generation X (even if your birth year is part of the Boom). Of course don't forget that no matter what year a specific individual is born, it doesn't mean they MUST be like their generation.
I would love to see the quantitative research use generational dividing lines that are rooted in historical theory, rather than birth rates. I know it's not objective, but wouldn't it be interesting to see whether or not the data matched up with the theory?