That sounds interesting. I've often wondered if the growth in use of the terms (mostly by younger people ime) has been due to an increased recognition of a "spectrum" (and therefore more diagnoses?) and more "inclusion" in mainstream schools.
I wouldn't necessarily associate that with a "loss" of stigma or misunderstanding though.
Not the only reason by any stretch, but a lot of stigma exists because we generally like to define people by their condition - a "diabetic", an "aspie" a "pschizophrenic" etc, rather than a person diagnosed with "x,y or z".