For words that only have three letters, there isn't any 4th letter. For instance with the word “increase”, there won't be any a lot more letters Later on and so have to be the word "include". The word “addict” is while in the BIP39 wordlist however, you might have used https://e-bookmarks.com/story4452923/facts-about-bip39-seed-phrase-word-list-revealed