For words that have only three letters, there is absolutely no 4th letter. Such as with the word “insert”, there won't be any far more letters afterwards and thus has to be the word "include". The word “addict” is within the BIP39 wordlist but you would've utilized “addi” for “addict”. https://thefairlist.com/story9057047/examine-this-report-on-bip39-mnemonic-phrase-tool