For words that have only 3 letters, there's no 4th letter. Such as with the word “include”, there aren't any a lot more letters afterwards and so need to be the word "add". The word “addict” is within the BIP39 wordlist however, you would've applied “addi” for “addict”. Art is https://classifylist.com/story21295308/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool