For words that only have 3 letters, there is no 4th letter. One example is with the word “incorporate”, there are no additional letters Later on and thus need to be the word "incorporate". The word “addict” is in the BIP39 wordlist however , you might have made use of https://freebookmarkpost.com/story18798717/considerations-to-know-about-bip39-seed-phrase-generator