For words that have only 3 letters, there is no 4th letter. As an example with the word “include”, there isn't any far more letters afterwards and so needs to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you would've employed “addi” for “addict”. This https://gorillasocialwork.com/story20486173/facts-about-bip39-seed-phrase-github-revealed