For words that only have three letters, there is no 4th letter. For instance with the word “insert”, there aren't any additional letters afterwards and thus has to be the word "insert". The word “addict” is inside the BIP39 wordlist but you would've employed “addi” for “addict”. Standard recovery phrases https://7bookmarks.com/story18726989/considerations-to-know-about-bip39-seed-phrase-generator