For words that have only three letters, there isn't a 4th letter. For example with the word “include”, there aren't any a lot more letters Later on and therefore needs to be the word "add". The word “addict” is within the BIP39 wordlist but you would've utilised “addi” for “addict”. https://rotatesites.com/story20034461/a-review-of-bip39-passphrase