For words that have only 3 letters, there is not any 4th letter. One example is with the word “include”, there are no more letters Later on and so need to be the word "incorporate". The word “addict” is from the BIP39 wordlist however you would've employed “addi” for “addict”. https://bookmarkinglog.com/story18916700/the-5-second-trick-for-ledger-seed-phrase-bip39