If you don’t have too many words known, you can go to the Vocabulary page and change the ranking of the words accordingly ? might be a bit of work but you can probably do it in small batches once per week?
Yea, your Vocabulary page idea is the best if you have a lot of bogus known words to edit. That’s what I did when the “mark known on exit” thing caught me once.
Also I end up changing words from known to 1 any time I can’t recall the word at all. Sometimes I’ll be reading the same word later and I immediately know it so I might change it back to known, but no harm in just leaving it at 1 (I never use the other numbers).
I think the reason I can’t recall a word, then later recall it with ease has everything to do with context. It’s not worth getting too anal about marking words. The tool is meant to help, not to enforce some behavior. Use it anyway you want.