For words that have only three letters, there's no 4th letter. One example is with the word “incorporate”, there aren't any much more letters Later on and therefore must be the word "include". The word “addict” is from the BIP39 wordlist however, you would've made use of “addi” for “addict”. https://socialfactories.com/story4276950/facts-about-bip39-seed-phrase-github-revealed