For words that only have 3 letters, there is not any 4th letter. As an example with the word “add”, there won't be any a lot more letters Later on and so has to be the word "increase". The word “addict” is in the BIP39 wordlist however, you would have https://getsocialnetwork.com/story4320895/the-5-second-trick-for-ledger-seed-phrase-bip39