“Generally, variables associated with knowledge at the lexical level versus those associated with use need to be better defined.”

These studies do a decent job of showing that people who know a lot of curse words generally have good overall vocabularies. I am sure I could write down just about every imaginable English curse word, and many in other languages, if given a pencil and paper and adequate time. However, I very rarely actually use a curse word in everyday speech, and these studies do a terrible job of distinguishing between those who know the words and those who use the words.