For words that only have 3 letters, there's no 4th letter. For instance with the word “incorporate”, there are no far more letters Later on and therefore have to be the word "include". The word “addict” is while in the BIP39 wordlist however , you would've utilized “addi” for “addict”. https://esocialmall.com/story4347602/little-known-facts-about-bip39-words