For words that have only 3 letters, there isn't a 4th letter. By way of example with the word “include”, there are no more letters Later on and so have to be the word "include". The word “addict” is from the BIP39 wordlist however , you might have used “addi” https://topsocialplan.com/story4424634/how-much-you-need-to-expect-you-ll-pay-for-a-good-valid-bip39-seed-phrase