For words that only have three letters, there is not any 4th letter. Such as with the word “include”, there isn't any additional letters afterwards and thus should be the word "incorporate". The word “addict” is inside the BIP39 wordlist however , you would have utilised “addi” for “addict”. Mnemonic https://bookmarkize.com/story19056062/new-step-by-step-map-for-bip39-english-words