For words that only have three letters, there's no 4th letter. One example is with the word “include”, there isn't any extra letters afterwards and so have to be the word "add". The word “addict” is from the BIP39 wordlist but you might have utilized “addi” for “addict”. Tips on https://thebookmarkage.com/story18796959/the-definitive-guide-to-bip39-seed-phrase