When I'm trying to spell a word that charm doesn't like and it auto corrects it, I find myself deleting it and retyping it when I get auto corrected again, then deleting it. After the second time, it seems like if I were to try to do it again, Charm is not able to pick up on the auto correction. I then miss out on this chance to add that word to my dictionary, with no way to reliably reproduce it again and even if I were to try to reproduce it again, it really slows down my workflow.
A suggestion to be would be that there are certain circumstances when add to dictionary pops up (this only happens to me for the first word of a sentence for some reason ) if someone deletes the same thing twice, that could be an opportunity to prompt them to add to dictionary also