For words that have only 3 letters, there isn't any 4th letter. For instance with the word “incorporate”, there aren't any extra letters afterwards and so has to be the word "add". The word “addict” is while in the BIP39 wordlist however you would've utilised “addi” for “addict”. Art is https://thesocialroi.com/story8555487/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition