For words that only have 3 letters, there is not any 4th letter. For example with the word “incorporate”, there are no extra letters afterwards and so needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you would've utilised “addi” for “addict”. Retail outlet https://bookmarkingdelta.com/story18768579/getting-my-bip39-words-to-numbers-to-work