For words that have only three letters, there isn't a 4th letter. One example is with the word “include”, there are no additional letters Later on and so should be the word "include". The word “addict” is within the BIP39 wordlist however , you would've used “addi” for “addict”. An https://bookmarkfly.com/story19489636/new-step-by-step-map-for-ledger-seed-phrase-bip39