For words that have only three letters, there is not any 4th letter. For example with the word “include”, there are no more letters afterwards and thus must be the word "add". The word “addict” is from the BIP39 wordlist however, you would've applied “addi” for “addict”. This informative article https://classifylist.com/story20591258/a-review-of-bip39-passphrase