For words that have only 3 letters, there isn't any 4th letter. For instance with the word “increase”, there aren't any additional letters Later on and thus need to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you might have utilised “addi” for “addict”. You https://www.storeboard.com/blogs/beauty-and-fashion/opening-the-globe-of-bip39-a-comprehensive-guide-to-mnemonic-expressions-and-word-checklists/6026188