For words that only have 3 letters, there's no 4th letter. For instance with the word “incorporate”, there won't be any far more letters afterwards and so needs to be the word "incorporate". The word “addict” is while in the BIP39 wordlist but you might have used “addi” for “addict”. https://thegreatbookmark.com/story18845459/getting-my-bip39-words-to-numbers-to-work