For words that have only three letters, there is not any 4th letter. One example is with the word “incorporate”, there are no far more letters afterwards and therefore needs to be the word "add". The word “addict” is within the BIP39 wordlist however , you would have applied “addi” https://natural-bookmark.com/story18919645/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39