For words that only have three letters, there is not any 4th letter. Such as with the word “include”, there aren't any extra letters afterwards and so needs to be the word "add". The word “addict” is from the BIP39 wordlist however, you might have utilized “addi” for “addict”. This https://tealbookmarks.com/story19456175/considerations-to-know-about-bip39-seed-phrase-generator