Micro-Syntactic Variation in North American English

Is "I believe ain't nobody leavin'" ungrammatical? Maybe, apparently, it all depends on micro-syntax.

http://www.slate.com/blogs/lexicon_valley/2015/06/29/the_yale_grammatical_divers...

http://microsyntax.sites.yale.edu/phenomena

An interesting article. Seems to hinge on your idea of whether grammar is inherent to a language, or inherent to an individual's understanding of how to communicate. When enough individuals share a given rule, it becomes its own grammar (regional or "micro-syntax"), as opposed to being an instance of people not speaking correctly.

I've always tended to the latter view: if you're understood, you're speaking "correctly". Speaking inappropriately for the social context is relevant, but is different from the question of correct / incorrect usage. But I know, that implies every mistake is also always a potential new micro-syntax in development ....