For words that have only three letters, there's no 4th letter. For example with the word “include”, there isn't any additional letters afterwards and therefore should be the word "add". The word “addict” is inside the BIP39 wordlist but you would have made use of “addi” for “addict”. To try https://allyourbookmarks.com/story18857087/invalid-bip39-phrase-things-to-know-before-you-buy