For words that have only three letters, there is not any 4th letter. Such as with the word “include”, there are no additional letters Later on and therefore need to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you might have made use of “addi” https://freshbookmarking.com/story19043234/the-definitive-guide-to-bip39-seed-phrase