For words that have only three letters, there's no 4th letter. As an example with the word “include”, there are no additional letters afterwards and thus needs to be the word "increase". The word “addict” is inside the BIP39 wordlist but you would've applied “addi” for “addict”. Yet another benefit https://listingbookmarks.com/story18926607/a-review-of-bip39-passphrase