Example of false negative:
http://altwall.net/texts.php?show=bullet&number=2642

The main content doesn't use <p>. It's just some text nodes wrapped in <center>. The heuristics used by Mozilla Firefox is not very helpful here.

False negative for mozScore:
https://tw.mobi.yahoo.com/sports/%E5%A4%8F%E5%AD%A3%E8%81%AF%E8%B3%BD-%E6%9E%97%E6%9B%B8%E7%B7%AF%E9%81%A9%E6%87%89%E8%89%AF%E5%A5%BD-%E9%A1%8F%E8%A1%8C%E6%9B%B8-%E4%BB%96%E5%BE%97%E5%AD%B8%E8%91%97%E7%95%B6cp3-125812028.html

CJK might need a multiplier when counting length of textContent.

False negative for mozScore:
http://www.quenoticiasmaslocas.com/2015/09/razones-por-las-que-los-hombres-son.html

The main article doesn't have <p> tags.

Another example supporting multiplier for CJK.
http://tw.yangzhu6.com/v-zai-834993.html

False positive (a forum):
http://www.spanishdict.com/answers/122779/what-does-the-word-mejores-mean-in-spanish

  From user feedback:
  https://feedback.corp.google.com/product/282/neutron?lView=rd&lReport=10242704994

False positive (web comic):
http://www.geekculture.com/joyoftech/joyarchives/2293.html

  From user feedback:
  https://feedback.corp.google.com/product/282/neutron?lView=rd&lReport=9357710554

Another case that the main article doesn't have <p> tags like #c3:
http://www.gadgetsnow.com/tech-news/Apple-CEO-Tim-Cook-wishes-Happy-Diwali-shares-Indian-photographers-photos/articleshow/55139077.cms

You started fixing this bug over two years ago. Are you still working on it? You can update the status to "archived", "wontfix", or "closed". You can remove yourself as owner and change status to "untriaged", but if this is still a real bug, please do not sit on it.