For words that have only 3 letters, there's no 4th letter. One example is with the word “incorporate”, there aren't any more letters afterwards and therefore has to be the word "add". The word “addict” is while in the BIP39 wordlist but you would have applied “addi” for “addict”. To https://bookmarkoffire.com/story18746735/5-simple-techniques-for-bip39-word-list-pdf