Interesting, I could have written a post with exactly the same title. There have been quite a lot of occasions where I have used vocab I have learned through WK and my wife (or coworkers or customers or whoever is sitting next to me at my local watering hole) has had no idea what the word is, or at least not at first.
About 1/3 of the time she does know the word, just did not get what I was trying to say and lets me know that “We/Japanese people never use that word” and then teaches me the word(s) that would be used. So useful exercise for sure.
About 1/3 of the time she does know the word, just did not get what I was trying to say and lets me know that “Maybe my grandparents, or great grandparents, would have used that word” or “that is a very old and rarely used word”. Again I get a lesson on the word(s) she thinks shoud be used.
Of course, in both of those cases, they are words she does know, they just are not used much, or at all (depending on who is correcting me).
Of the remaining1/3, about half of the time she is convinced I am making a mistake (see note below) and I am sure I have pronounced it correctly and I look it up in a dictionary to show her. When she sees it in Kanji she goes “Oh yeah, sure that is what the word means, but I have never heard it used before” sometimes with “it might be used in some old writing sometimes”. The other half of the 1/3, after looking up the word in a dictionary, or writing it out (typing actually - aside from my name in katakana I do not handwrite at all) in Kanji she will inform me it is the first time she has ever seen it.
Note: To be fair (and honest full disclosure) it is more often the case that I have indeed made a mistake and ended up pronouncing a word that does not exist or is actually something else entirely.
Sometimes, if I really like a particular word, I insist on using it in conversation (at home with her)… just because. She will correct me a couple of times then just switch to calling me various versions of crazy or idiot
On a couple of occasions, when I have repeatedly made the same mistake over and over again and ending up making up a new word, it has just entered our private vocabulary and we both sometimes use it, as an inside joke.