For words that have only 3 letters, there is no 4th letter. As an example with the word “add”, there are no extra letters afterwards and so need to be the word "include". The word “addict” is during the BIP39 wordlist however you would've utilized “addi” for “addict”. In this https://bookmarkprobe.com/story19129241/new-step-by-step-map-for-ledger-seed-phrase-bip39