For words that only have three letters, there's no 4th letter. For instance with the word “increase”, there isn't any far more letters Later on and thus needs to be the word "insert". The word “addict” is while in the BIP39 wordlist however you would've utilized “addi” for “addict”. This https://web.archive.org/web/20241223212827/http://bip39-phrase.com/