Thank you for the comprehensive explanation.

I had to change my 'long held belief' that vocabualry (from 'vocable': voice-able; utterance (including 'words' or diction (which gives rise to 'dictionary': all that express diction: articulation of words).

In short, 'eek, yak, yum,...' are (vocable) included in vocabulary but may not be included in 'diction' or dictionary because they don't have 'formal' ways to pronounce exactly.

I was wrong apparently ;-)