For words that have only three letters, there isn't a 4th letter. For example with the word “insert”, there aren't any more letters Later on and thus needs to be the word "include". The word “addict” is within the BIP39 wordlist however you would have utilized “addi” for “addict”. Artwork https://socialrus.com/story18309583/a-review-of-bip39-phrase-list