For words that have only 3 letters, there is not any 4th letter. For example with the word “incorporate”, there are no extra letters afterwards and so needs to be the word "include". The word “addict” is inside the BIP39 wordlist but you would've used “addi” for “addict”. By pursuing https://socialeweb.com/story4878190/bip39-phrase-generator-can-be-fun-for-anyone