For words that only have three letters, there is not any 4th letter. As an example with the word “include”, there isn't any extra letters afterwards and so have to be the word "increase". The word “addict” is during the BIP39 wordlist but you would have used “addi” for “addict”. https://peakbookmarks.com/story19225079/new-step-by-step-map-for-ledger-seed-phrase-bip39