Question: on the treatment of the lexicon as possessing an absolute extent and content

I am curious whether there is a terminology or framework for addressing the extent to which the speakers of a language deem a lexicon to have absolute definition regardless of reference to a specific source of authority on the subject. That is to say for example, the extent to which the phrases “that is a word” and “that is not a word” are regarded as wholly meaningful assertions, with respect to speech.

Surely, there’s likely to be a strong correlation between this sort of treatment of vocabulary as strictly defined inventory of the language, and the formalisation and inventorying of the language via lexicography per se. But I am disinclined to believe that, e.g., speakers of unwritten languages cannot have a sense of the relative inclusivity or exclusivity of their language’s vocabulary, or that, conversely, languages with a written lexicon cannot demonstrate flexibility and variability with respect to their appreciation of a distinction between an utterance generally, and a “word”.

Is there a framework (e.g., a good piece of written theory), or even just a few key definitions, which facilitate the discussion of the way in which speakers conceptualise their lexicon, especially with respect its having a strict extent and sense of inclusivity or exclusivity?