For words that have only 3 letters, there is no 4th letter. By way of example with the word “incorporate”, there are no additional letters afterwards and so has to be the word "add". The word “addict” is while in the BIP39 wordlist but you might have used “addi” for https://bookmarkedblog.com/story19566985/the-5-second-trick-for-ledger-seed-phrase-bip39