For words that have only 3 letters, there's no 4th letter. For instance with the word “incorporate”, there aren't any more letters Later on and thus have to be the word "add". The word “addict” is within the BIP39 wordlist however, you would have utilised “addi” for “addict”. Meticulously overview https://highkeysocial.com/story4279209/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition