For words that have only three letters, there is absolutely no 4th letter. For instance with the word “incorporate”, there won't be any additional letters afterwards and thus should be the word "increase". The word “addict” is while in the BIP39 wordlist but you would have used “addi” for “addict”. https://guideyoursocial.com/story4045259/examine-this-report-on-bip39-mnemonic-phrase-tool