For words that have only three letters, there isn't a 4th letter. One example is with the word “incorporate”, there are no a lot more letters afterwards and so must be the word "incorporate". The word “addict” is inside the BIP39 wordlist however you would have made use of “addi” https://travialist.com/story9718521/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39