For words that only have three letters, there is no 4th letter. For example with the word “incorporate”, there isn't any much more letters Later on and therefore must be the word "add". The word “addict” is during the BIP39 wordlist however you would've made use of “addi” for “addict”. https://iowa-bookmarks.com/story15250386/considerations-to-know-about-bip39-seed-phrase-generator