For words that have only 3 letters, there is no 4th letter. For instance with the word “insert”, there are no a lot more letters afterwards and so should be the word "insert". The word “addict” is within the BIP39 wordlist but you might have applied “addi” for “addict”. A https://active-bookmarks.com/story19510366/bip39-phrase-generator-can-be-fun-for-anyone