For words that have only three letters, there is not any 4th letter. One example is with the word “incorporate”, there aren't any extra letters Later on and thus should be the word "incorporate". The word “addict” is from the BIP39 wordlist but you would have utilized “addi” for “addict”. https://socialbaskets.com/story5205366/not-known-facts-about-bip39-english-words