For words that have only 3 letters, there isn't any 4th letter. For example with the word “include”, there are no a lot more letters Later on and therefore must be the word "insert". The word “addict” is within the BIP39 wordlist however , you would've applied “addi” for “addict”. https://hotbookmarkings.com/story18818212/5-simple-techniques-for-bip39-seed-phrase