It seemed like my misunderstanding was thinking that concubinage was more consensual that it appears to be. Shows you what you get for thinking in the abstract sometimes (my working definition was just "institutionalized affairs for the powerful", without any of the typical context).
Hmm, for some cultures, the English word concubine (as it would be translated) actually denotes a highly respected position for someone who would otherwise be low status. I think in some Asian cultures these women were supposed to help bear heirs for the king, and they lived very well compared to their non-concubine peers. Probably not strictly consensual, but monarchy is often a situation where 'everyone' was basically a slave to the monarch, no matter who you were.
It's the broader term in general, which is why I picked it over "mistress" originally despite the usual negative connotations (like how "witch" is usually negative... except when it's not). Then again, I also mentioned blood brothers as another ancient relationship status, and somehow we're not talking about that. So I don't understand my own derail and... yeah, I should probably shut up and go to work, heh heh. 8^)
[ETA:] Actually, I have an on-topic question!
Is it a bug that kobolds steal from vaults, or are they really that badass?