For words that have only 3 letters, there isn't a 4th letter. For example with the word “incorporate”, there are no extra letters Later on and therefore has to be the word "include". The word “addict” is inside the BIP39 wordlist however, you would've applied “addi” for “addict”. Mnemonic words https://wearethelist.com/story20917732/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator