For words that only have three letters, there isn't any 4th letter. For example with the word “include”, there are no much more letters afterwards and thus needs to be the word "insert". The word “addict” is while in the BIP39 wordlist but you might have applied “addi” for “addict”. https://thebookmarklist.com/story18803851/fascination-about-bip39-english-words