For words that have only three letters, there is absolutely no 4th letter. For example with the word “incorporate”, there aren't any extra letters afterwards and so has to be the word "include". The word “addict” is within the BIP39 wordlist but you would have made use of “addi” for https://bookmarkshome.com/story4445616/examine-this-report-on-bip39-mnemonic-phrase-tool