For words that only have 3 letters, there isn't a 4th letter. For example with the word “include”, there isn't any far more letters afterwards and thus has to be the word "incorporate". The word “addict” is while in the BIP39 wordlist however you would have employed “addi” for “addict”. https://kbookmarking.com/story18851416/bip39-seed-phrase-fundamentals-explained