For words that have only 3 letters, there isn't a 4th letter. By way of example with the word “include”, there isn't any far more letters Later on and thus must be the word "insert". The word “addict” is within the BIP39 wordlist however, you would've applied “addi” for “addict”. https://total-bookmark.com/story18784979/the-ultimate-guide-to-bip39-seed-phrase-github