For words that only have 3 letters, there isn't any 4th letter. For instance with the word “increase”, there isn't any a lot more letters afterwards and thus needs to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however you would have made use of “addi” https://bookmarkspy.com/story20427346/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool