For words that have only 3 letters, there is not any 4th letter. One example is with the word “include”, there aren't any more letters afterwards and so should be the word "insert". The word “addict” is inside the BIP39 wordlist however, you would have made use of “addi” for https://leftbookmarks.com/story18911530/new-step-by-step-map-for-ledger-seed-phrase-bip39