For words that have only 3 letters, there is absolutely no 4th letter. For instance with the word “insert”, there won't be any much more letters Later on and thus need to be the word "include". The word “addict” is from the BIP39 wordlist but you might have utilized “addi” https://bookmarkize.com/story19634015/the-greatest-guide-to-seed-phrase-bip39