... and their levels C1 or C2 and so on?
I should perhaps explain a couple more things about word lists and learner's dictionaries.
1) You don't see words listed as C1 or C2. Many publishers have a separate version, usually called an
advanced learner's dictionary for more advanced learners.
2) The level 'rating' of each word is based solely on frequency, as shown by corpus data. That is because the most frequent words that people use are considered to be priorities for learners who are starting out to learn the language. The usual estimation is that to get up to, say, C1, a learner should need to know the most common 5000 or so words in the language—thus Oxford's famous
Oxford 5000.
Once a learner reaches C1 or beyond, the association between competence (i.e., level) and number of acquired words (i.e., active and passive vocabulary) begins to weaken very quickly. At such high levels, it's really about what you can do with the language, not about how many words you know.