For words that only have 3 letters, there isn't any 4th letter. One example is with the word “include”, there won't be any much more letters afterwards and therefore should be the word "insert". The word “addict” is within the BIP39 wordlist however, you might have applied “addi” for “addict”. http://andersonsaeu988.iamarrows.com/from-mnemonics-to-safety-and-security-recognizing-bip39-passphrases-and-their-significance-in-copyright