For words that have only three letters, there is not any 4th letter. Such as with the word “increase”, there isn't any additional letters afterwards and so has to be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you would have utilised “addi” for “addict”. Standard https://modernbookmarks.com/story19267245/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool