Hi Amanda,
From my testing on the Digital Channels, here's what I have seen:
Support Center: Search for Phrase. No Article Match

Knowledge Widget: Search for an Article. No Article Match
Digital Bot: User search and No Match triggered. Or, Search results in multiple options and user presses "None of these"

As for your second question, I don't know of a way to clear the unanswered queries. The only thing I can think of beyond that is to create an unpublished article and associate those other phrases to that artcle. It allows you to at least clear those queries...? I haven't test this idea yet, but I can't think of anything else.
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Peter Stoltenberg
TTEC Digital
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