For words that only have three letters, there is absolutely no 4th letter. Such as with the word “insert”, there isn't any extra letters Later on and thus has to be the word "incorporate". The word “addict” is within the BIP39 wordlist however, you would've employed “addi” for “addict”. Art https://apollobookmarks.com/story18790640/little-known-facts-about-bip39-words