For words that only have three letters, there's no 4th letter. One example is with the word “incorporate”, there isn't any additional letters afterwards and so must be the word "insert". The word “addict” is while in the BIP39 wordlist however you would've employed “addi” for “addict”. If you're Uncertain https://allyourbookmarks.com/story18961346/little-known-facts-about-bip39-words