For words that have only 3 letters, there isn't a 4th letter. By way of example with the word “include”, there isn't any far more letters afterwards and so have to be the word "add". The word “addict” is from the BIP39 wordlist but you would've employed “addi” for “addict”. https://onlybookmarkings.com/story18737952/not-known-factual-statements-about-bip39-explained