“The rest of the labels are made up, in my opinion.”
All of the “generation labels”, including that of “baby boomers”, are categories that were invented by marketing agencies.
“Baby boomer” originally was used by store buyers and merchandisers and ad agencies as shorthand in their marketing plans. A term of convenience. At some point it bled over into general circulation articles and everybody began using it.
The current trend is to divide the baby boomer generation into two parts, instead of letting it run from 1946 to 1964. Now “boomers” are the 1946-1954 cohort and “Generation Jones” runs from 1954-1965.