For words that have only three letters, there is no 4th letter. By way of example with the word “insert”, there aren't any more letters Later on and so has to be the word "include". The word “addict” is while in the BIP39 wordlist but you would've applied “addi” for https://peakbookmarks.com/story19226590/the-5-second-trick-for-ledger-seed-phrase-bip39