For words that only have three letters, there is no 4th letter. Such as with the word “include”, there aren't any a lot more letters afterwards and thus needs to be the word "insert". The word “addict” is while in the BIP39 wordlist however, you would've applied “addi” for “addict”. https://xyzbookmarks.com/story18826463/the-greatest-guide-to-seed-phrase-bip39