For words that have only three letters, there is no 4th letter. Such as with the word “incorporate”, there are no additional letters Later on and therefore must be the word "incorporate". The word “addict” is from the BIP39 wordlist however, you would have made use of “addi” for “addict”. https://bookmarkbells.com/story18866848/the-2-minute-rule-for-bip39-all-words