For words that only have 3 letters, there is no 4th letter. For instance with the word “incorporate”, there isn't any more letters Later on and thus must be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you would've made use of “addi” for “addict”. You https://thegreatbookmark.com/story18847944/phrases-with-bit-an-overview