For words that only have three letters, there's no 4th letter. For example with the word “increase”, there aren't any more letters afterwards and so need to be the word "include". The word “addict” is during the BIP39 wordlist however you would've utilised “addi” for “addict”. Standard recovery phrases use https://hotbookmarkings.com/story18821111/5-essential-elements-for-bip39-explained