For words that only have 3 letters, there is not any 4th letter. For instance with the word “include”, there aren't any more letters afterwards and thus need to be the word "include". The word “addict” is from the BIP39 wordlist however, you would've applied “addi” for “addict”. BIP39 and https://mediajx.com/story21495758/an-unbiased-view-of-bip39-seed-phrase-github