Good question. I think if you declared that instead of saying "red", we now all said "butterfinger", it's not that it would be illegitimate, but if it didn't gain any momentum you'd be hard pressed to say that it was part of the language. However, the appropriation of jawn (which is implied to be working class vernacular) by white hipsters or whatever the original comment said could cause some consternation, but if it catches on, than I'd argue it's now just part of the language (what I called 'legitimate' in my original post).

yep -- first time I heard it was on Dj Jazzy Jeff & The Fresh Prince's "I'm All That" circa 1991. "...set my sights on making a record that people thought was a hype jawn." I was living in New England at the time and all the middle school kids [including me] started saying it shortly thereafter.

We generally assumed it was a synonym for "joint" [as described in the linked article] in the sense of "unit of work," e.g. "A Spike Lee Joint"

[p.s. for the record, "Homebase" is an outstanding LP that still sounds great today]

As someone who grew up in the area, I mostly recall it being used in the late 90s, then not really that often afterwards.