Are the infrequently used words really that infrequent? Can I trust the list of frequently used words?

First of all, thanks to the developers for creating language reactor. It is an extremely helpful tool. I’d like to go ahead and focus on learning the commonly used words in the provided list of words. However I’m noticing that a fair number of “infrequently used words” are not actually that uncommon. I should specify that I’m studying Korean. Actually I’ve been living in Korea and studying the language for about 5 years now, so I feel like I have some sense of what words are commonly used. That said, I’m curious how language reactor determined what words are frequently used and what words are not frequently used. For simplicity sake, I’d like to just focus on learning the recommended, frequently-used words. However, my concern is that, if I just focus on the commonly used words, I’ll miss out on other important words, since there appears to be a number of fairly common words that are marked as “infrequently used.” Any thoughts or advice here?