For words that have only three letters, there isn't a 4th letter. For instance with the word “include”, there are no much more letters Later on and therefore should be the word "add". The word “addict” is while in the BIP39 wordlist however, you might have made use of “addi” https://nybookmark.com/story20641448/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool