For words that have only 3 letters, there is absolutely no 4th letter. One example is with the word “include”, there aren't any much more letters Later on and thus need to be the word "include". The word “addict” is within the BIP39 wordlist however , you would have applied https://bookmarklogin.com/story18963278/little-known-facts-about-bip39-seed-phrase-list