For words that only have three letters, there isn't a 4th letter. Such as with the word “include”, there are no extra letters afterwards and thus has to be the word "add". The word “addict” is during the BIP39 wordlist however you would have applied “addi” for “addict”. Mnemonic words https://kingbookmark.com/story18972496/examine-this-report-on-bip39-mnemonic-phrase-tool