For words that only have three letters, there is no 4th letter. For example with the word “incorporate”, there aren't any a lot more letters Later on and therefore need to be the word "add". The word “addict” is while in the BIP39 wordlist however you would have made use https://thesocialcircles.com/story4701988/getting-my-bip39-words-to-numbers-to-work