For words that have only three letters, there is no 4th letter. For example with the word “incorporate”, there isn't any additional letters Later on and therefore has to be the word "include". The word “addict” is within the BIP39 wordlist however, you would've applied “addi” for “addict”. Several Wallets:In https://getsocialnetwork.com/story4514579/the-greatest-guide-to-seed-phrase-bip39