For words that only have 3 letters, there is no 4th letter. One example is with the word “include”, there won't be any a lot more letters Later on and thus need to be the word "add". The word “addict” is from the BIP39 wordlist however you would've used “addi” https://getsocialselling.com/story4563713/helping-the-others-realize-the-advantages-of-bip39-seed-phrase-mnemonics-generator