For words that have only 3 letters, there isn't any 4th letter. As an example with the word “incorporate”, there won't be any extra letters Later on and therefore has to be the word "incorporate". The word “addict” is within the BIP39 wordlist however , you might have utilized “addi” https://1001bookmarks.com/story18791622/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting