For words that have only three letters, there's no 4th letter. For example with the word “include”, there aren't any much more letters Later on and so has to be the word "incorporate". The word “addict” is while in the BIP39 wordlist however , you would've utilized “addi” for “addict”. https://socialfactories.com/story4495994/a-review-of-bip39-passphrase