This used to actually be fairly normal (at least, within the realm of taboo social sex activities), its where the term ‘swingers’ originally came from, way back in the 50s/60s.
According to "The Lifestyle: A Look at the Erotic Rites of Swingers" (Gould, 1999), key clubs originated with WWII pilots, but entered the lexicon as key parties in the 50s and 60s. However, all the academic study is based on secondhand accounts. It's the kind of thing that leads me to wonder if "key party" was some kind of Urban Dictionary expression with someone making up the term for giggles. The expression entered the lexicon and some people then tried it out, i.e. the vocabulary preceded the social trend.
Non-monogamy does seem to be the human norm, and it's a bummer there's so much unnecessary taboo and complexity wrapped up in non-monogamy.
I also fully accept that we're just not moving in the correct circles for our goals. Working on it!
I love when old(er) folk have great adventures and anecdotes to share. And proceed to share them.
That qualification gave me a good chuckle. Thanks, cheers, and enjoy your holiday!