For words that have only three letters, there isn't any 4th letter. Such as with the word “add”, there isn't any far more letters Later on and so has to be the word "include". The word “addict” is while in the BIP39 wordlist however, you would've used “addi” for “addict”. https://getidealist.com/story21403798/the-basic-principles-of-bip39-passphrase-generator