For words that have only 3 letters, there is not any 4th letter. Such as with the word “insert”, there are no far more letters afterwards and so must be the word "insert". The word “addict” is in the BIP39 wordlist however , you might have utilized “addi” for “addict”. https://telebookmarks.com/story9251617/the-invalid-bip39-phrase-diaries