For words that only have 3 letters, there's no 4th letter. For instance with the word “include”, there won't be any a lot more letters afterwards and so have to be the word "include". The word “addict” is during the BIP39 wordlist however, you would have applied “addi” for “addict”. https://bookmarkdistrict.com/story18709973/the-invalid-bip39-phrase-diaries