For words that only have three letters, there's no 4th letter. By way of example with the word “incorporate”, there aren't any far more letters afterwards and thus need to be the word "incorporate". The word “addict” is while in the BIP39 wordlist however you would've employed “addi” for “addict”. https://yourbookmarklist.com/story19071549/an-unbiased-view-of-bip39-seed-phrase-github