For words that have only three letters, there is absolutely no 4th letter. One example is with the word “include”, there won't be any additional letters afterwards and thus must be the word "insert". The word “addict” is from the BIP39 wordlist but you would've utilized “addi” for “addict”. You https://bookmarkick.com/story18904477/examine-this-report-on-bip39-mnemonic-phrase-tool