For words that only have 3 letters, there is not any 4th letter. By way of example with the word “add”, there isn't any far more letters Later on and therefore need to be the word "add". The word “addict” is from the BIP39 wordlist but you might have used https://advicebookmarks.com/story26405112/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting