For words that have only three letters, there is not any 4th letter. Such as with the word “increase”, there isn't any extra letters afterwards and so needs to be the word "include". The word “addict” is inside the BIP39 wordlist however you would have employed “addi” for “addict”. In https://johsocial.com/story9371323/little-known-facts-about-bip39-seed-phrase-list