For words that have only three letters, there is absolutely no 4th letter. By way of example with the word “incorporate”, there isn't any a lot more letters afterwards and therefore have to be the word "include". The word “addict” is within the BIP39 wordlist but you would've applied “addi” https://bookmarkity.com/story19110448/ledger-seed-phrase-bip39-no-further-a-mystery