For words that have only 3 letters, there isn't a 4th letter. One example is with the word “insert”, there are no additional letters Later on and thus should be the word "include". The word “addict” is in the BIP39 wordlist however , you might have employed “addi” for “addict”. https://bookmarklinx.com/story18918385/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news