For words that only have three letters, there isn't a 4th letter. For instance with the word “increase”, there isn't any extra letters Later on and therefore must be the word "include". The word “addict” is from the BIP39 wordlist however, you would have utilized “addi” for “addict”. Using BIP44 https://getsocialselling.com/story4902849/little-known-facts-about-bip39-words