For words that only have 3 letters, there isn't any 4th letter. For instance with the word “insert”, there are no extra letters Later on and therefore has to be the word "include". The word “addict” is within the BIP39 wordlist however , you would've applied “addi” for “addict”. Meticulously https://madesocials.com/story4953547/helping-the-others-realize-the-advantages-of-bip39-seed-phrase-mnemonics-generator