For words that only have three letters, there is no 4th letter. By way of example with the word “increase”, there are no much more letters Later on and thus needs to be the word "increase". The word “addict” is while in the BIP39 wordlist however you would have made https://modernbookmarks.com/story18621357/the-5-second-trick-for-ledger-seed-phrase-bip39