Well now that I went to Wiktionary and looked up the word polyamorous, I guess my excuse is I was born in 1968 (I'm not embarrassed to say that I didn't know what it meant).
English Alternative formspolyamourous (rare)
Etymology
The term dates from the 1960s or earlier, a hybrid of the Greek poly for many and the Latin amor for love.
Adjective
polyamorous (comparative more polyamorous, superlative most polyamorous)
Following one of various practices of having relationships with multiple partners, with the knowledge and consent of all involved. Having personal beliefs regarding relationships that are compatible with polyamory, regardless of one's experience or current practices.
Personally not sure how many stories are applicable to the that title though . Like Cia mentions, it is kind of hard for staff to read all the stories completely on site to ensure proper tagging or if such a relationship occurs in latter chapters, most wouldn't know but the readers. Also, as she mentions, she is the Admin overseeing Stories, and she is always open to ideas that can make the site better
Thanks for bringing it up LitLover