Here's the thing...
Tapas appears to have upgraded the search engine so episodic tags matter more ...BUT it coincides with Apple's search for "questionable" material. It's never really been confirmed or denied that this was Apple's initial flagging system but some creators who got flagged didn't label the episodes as mature but did have words in the episodic tags that could of been red flagged.
Beyond that, episodic tags seem to still rank low in the search engine. It prioritizes the word searched in series titles and author's name first. And somethings don't seem to appear in tag searches at all.