For words that only have 3 letters, there is not any 4th letter. For example with the word “increase”, there aren't any extra letters afterwards and thus needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you would've utilised “addi” for “addict”. Standard recovery https://yoursocialpeople.com/story4160104/bip39-seed-phrase-mnemonics-generator-an-overview