For words that have only 3 letters, there's no 4th letter. Such as with the word “add”, there aren't any far more letters afterwards and so must be the word "add". The word “addict” is inside the BIP39 wordlist but you might have made use of “addi” for “addict”. You https://bookmarkspiral.com/story18879773/not-known-facts-about-bip39-english-words