For words that have only three letters, there is not any 4th letter. For example with the word “include”, there are no extra letters afterwards and thus need to be the word "increase". The word “addict” is inside the BIP39 wordlist however, you would have made use of “addi” for https://mylittlebookmark.com/story4463296/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting