For words that have only 3 letters, there isn't any 4th letter. One example is with the word “incorporate”, there are no additional letters afterwards and so have to be the word "add". The word “addict” is during the BIP39 wordlist however, you would've used “addi” for “addict”. Getting just https://macrobookmarks.com/story19047101/invalid-bip39-phrase-things-to-know-before-you-buy