For words that only have three letters, there isn't any 4th letter. For example with the word “increase”, there aren't any far more letters Later on and thus needs to be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you might have used “addi” for “addict”. https://bookmarksystem.com/story18754026/a-review-of-bip39-passphrase