For words that have only 3 letters, there is not any 4th letter. One example is with the word “increase”, there aren't any extra letters afterwards and thus should be the word "increase". The word “addict” is inside the BIP39 wordlist but you would've utilized “addi” for “addict”. To test https://listbell.com/story8561781/examine-this-report-on-bip39-mnemonic-phrase-tool