For words that have only 3 letters, there is no 4th letter. Such as with the word “insert”, there won't be any much more letters afterwards and therefore should be the word "add". The word “addict” is from the BIP39 wordlist but you might have employed “addi” for “addict”. A https://bookmarkworm.com/story18781873/a-secret-weapon-for-bip39-words-to-numbers